Major difference in the '96 heads is the intake mounting bolt pattern - not
at all like the stock 6 x 3/8" bolts @ 90ø to the head per side on the SyTy. The 1996's mount via 4 x 5/16" bolts at entirely different places & angles. Casting number of the heads is "772", combustion chamber is heart shaped (better for knock resistance??).

BTW, the 96 gaskets seem to be rare items; might want to get a couple of
sets to allow for screwups & have a set on hand.

The following is how it went for me; techniques subject to change and YMMV:

To mount the new heads, you must either slot out the intake manifold to use the 1996 bolt holes (centermost holes = BIG slots), or plug & redrill & tap
the new heads. The second method is the one I used; those 4 x 5/16" bolts are *skimpy* looking; just feel better using those six big bolts. Less butchery to the manifold, too - it would look *ugly*.

The 1996 head manifold mounting holes need to be first plugged; the center
two can just be JB-Welded shut, as they are not near anything important.
The outer holes need to be plugged mechanically, as the redrilled holes for the SyTy bolts will pass through the holes. I cut a piece of 5/16" NC rod & JB Welded it into place @ each end of the head. Cut about 1" long w/ saw slot in the end so's you can tighten w/ a screwdriver. Goop (line) holes w/ JB, slowly screw studs into holes, bottom them out if possible. Screw in a bit more every few seconds; the JB has to flow out a bit. When set, grind filled holes down flush w/ the gasket surface.

Don't forget to drill & tap the two 1/4" x 20 holes for the dipstick support tube & ignition wire looms - this is easier to do *before* you mount the heads on the engine......}:{E These will be 'wet' holes, so sealer on the bolts is important. I used the grease/teflon thread sealer made by ARP (used on head bolts, also).

Good time to do any porting & polishing you want to do at this point, as well as get the valves ground, etc. Adding 2.02" & 1.60" valves will give very marginal improvement in breathing (if any), according to Fisher & Waar's book "How to Hotrod the SBC". 1996 valve sizes are 1.94" x 1.50"; really into less bang for the buck here (opinion totally my own). The Sy lower plenum will mismatch a good bit also, especially at the bottom. The upper edges will come out more or less even because of the manifold spacer. 

Ok, now what? Need to match up the ports as well as possible; the 1996 ports are sewer pipes compared to the SyTy's. Place the heads on the
engine w/ old set of head gaskets in place; bolt lightly in place w/ one or two bolts. The head gasket measures about 0.055" uncompressed; I didn't
have a used one handy (did this on a spare block), so's a piece of cardboard 0.040" thick was used (guessing @ compressed thickness). Install 1996 manifold gasket on heads - nicely lines up and retains w/ 2 plastic pins. Position manifold in approximately right place - WITH 3/16" SPACERS
BETWEEN MANIFOLD & GASKETS. The head ports actually lie outside the upper surface of the SyTy intake manifold - no seal is possible there just using a gasket; that's why the 3/16" spacing. Also, this will line up
the passages the best at the *top* of the manifold & head, giving the injector the best shot @ the intake valve. The spray will not actually *hit* the valve, but then, it never did stock, either. 
Insert distributor - this will sort of 'index' things correctly, position-wise. Notice that the distributor now sits about .40" higher than before - the oil pump drive shaft engagement is now nonexistent; more on this later. Make a 'feeler' tool to help line up the ports; a 1/2" section of carpenter's nail soldered to another nail (full length) in a "T" fashion will help. Using this tool inserted between the heads & manifold (& a flashlight), line up the ports as well as possible; try to equalize the mismatch evenly - it will be about 3/16" all around.

Finish your head work now: port matching, valves, seals, etc.
Ok, now we've got to take up that 3/16" space between the heads & manifold. I'm using acetal plastic sheet, which the manufacturer assures me will
work. Aluminum might be better but harder (for me) to cut as needed. Trace 96 gasket *ports* on sheet (cut to 2 3/4" x 15 1/4") & cut out ports.
Then, trace the *bolt holes* and water passage holes from a SyTy (or any pre-96 4.3) gasket on the acetal sheet after aligning the port openings.
I used a router table w/ 1/8" bit for cutting the port holes - cuts like butter. Drill the bolt holes 3/8". Trial assemble, file to fit as needed; make bolt holes slightly oversize for alignment. Roughen w/ 100 grit sandpaper side that will go towards manifold; acetal is very slick (feels like Teflon), need the 'bite' for adhesion. Run a small bead of epoxy on the spacers, 1/8" bead is more than enough. Run around ports, bolt holes,
anywhere that the plastic will touch the manifold. Use slow set stuff, not fast set, keep clamped to heads, lightly, w/ 3/8" x 1 1/4" bolts in mounting holes until initially set (about 1 hour). Disassemble before epoxy completely sets, otherwise, bolts may bond to the heads. Port match heads,
spacers & manifolds best as possible here, too - BIG differences, especially @ the bottom of the manifold runners. Be sure not to cut into gasket surface of spacer.

Distributor - measure gap between manifold & block before disassembling engine - should be 1/8" or so. Measure same gap w/ new heads on - probably around 0.40 larger" - need to set the distributor deeper in the now higher manifold by this amount. Oil pump drives off the end of distributor shaft, engagement here is kinda light to begin with, so check carefully. You could spot face the distributor mounting boss deeper by .4", or modify the distributor; I went this route. I turned (lathe) the clamping boss off the distributor entirely. A new boss was made from a piece of 1" pipe coupling (O.D. = 1 3/4"), and JB Welded into place. Measuring from the 'peak' of the *block* (behind the manifold) to the base of the distributor (the flange the cap mounts on) was 4.17" or so on mine; mounted to the raised manifold, this distance was now 4.55". Position the distributor to the old measurement, set the new clamping boss on the manifold & JB into place. A bead of fibrous window caulking around the distributor will keep the JB
from running down the distributor shaft. Beware - the distributor will now set lower on the manifold, getting at the clamp bolt will be even harder than before (is that even possible?); you'll need to grind that special 9/16" tool you made even thinner.
Run a big bead of silicone on the block manifold surface & let dry - this gap is now pretty big (close to 1/2"), so put on a second bead over it just before seating lower plenum.

The manifold is mounted w/ 3/8" x 16 x 1 1/4" bolts and the stock studs where used; check the lengths for bottoming - adjust length if needed, as well as the studs used to attach manifold, but they're right around 1 1/4" as is. Might want to use some 3/8" aircraft washers to adjust lengths if available. I'd go *light* on the torque here; use thread sealer on all to prevent loosening & prevent any possible leaking on the "wet" end holes. I used Locktite medium strength stuff, has good holding power, and the ARP sealer on the end bolts/studs.