I assume you meant "91 GMC 5.7 5 speed", and if so... I have this from another similar post on another forum.
I have a 5.3 and am planning on using a Muncie M20, I think the principle is the same. The devil is in the details.
From what I have read you need:
-Fly wheel from a 4.8 or 6.0
https://www.summitracing.com/parts/luk-lfw387
-Clutch kit for your trans (I need a 10 spline, yours may be different)
https://www.summitracing.com/parts/luk-04-049
-Something to do the clutching (I am using hydraulic but I cant imagine mechanical being bad)
https://www.summitracing.com/parts/hre-82870
-Pilot bearing for LS
https://www.summitracing.com/parts/ADO-CT1082
-Shifter (obvious, I know, but mine was a pain- Thanks Hurst)
-Bell housing: This may be tricky - or not. I am using a 6263756 truck housing. The distance from the older trans are .4"(?) further from the engine that the LS - something about the crank shaft flange. It depends on which crank you have will determine if you need to make adjustments. They make flywheels that are thicker, but they are $$$ (for me, at least).
I also had to use an adapter ring to mate the trans to the housing (
http://dennymac.com/muncie-bell-housing-adapter-ring)
- cross member mount: I made one
- VSS for the 5.3 computer
https://www.summitracing.com/parts/rpc-250-4153
Resources I use:
https://ls1tech.com/forums/conversio...-ls-motor.html
https://www.youtube.com/watch?v=RCGl5HbrUeE
I am using a Walbro external pump - not sure if the TBI has enough flow/pressure. I bet there are aftermarket kits - or maybe a stock one from a LS vehicle. There are returnless and two line fuel rails on the 5.3s
Radiator should be fine
I made my own motor mounts, but your application may have more options for pre-made
Use harness & computer from the 5.3, I used
https://www.facebook.com/pg/LT1-Swap...70183759682543 as a guide. I will also use them for my computer reflash until I can get it to a dyno shop.
Can't say about the pan. There are different ones depending on your 5.3, I have the truck one and it is wicked deep in the rear.
I bet the fan will work, I don't think the 5.3 will make more heat than the 5.3.
There are the gauges that may need researched - not sure if they will line up. And OBD2 port, but those are cheap.
EDIT: To be clear, I am still in the installation & parts finding phase and have not tested all of this.