I am going to pull the engine on my 89 to fix a lot of leaks and a cracked flexplate and I have a 91.5 ic parts truck and I was thinking about putting its bigger turbo on the 89 but really don't want to try and fit in the factory intercooler but I guess could put in a small IC under the hood somewhere... would I be gaining anything worthwhile? or just leave it be

 

Unless you are running high EGT, there is no need for a turbo "upgrade".
The stock NON intercooled turbo is good for most mild builds.
Installing a '91.5 turbo, if it is off an auto truck. would NOT be an upgrade, as it might have the LAGMASTER 21 CM exhaust housing on it.
This would make spool up …well - "lag".

 

I agree with OF and also you need to keep in mind that the tiny non i/c turbo is matched for the non i/c crossover pipe (low volume compared to the intercooled setup) So you will find that a 91.5+ I/C H1C with the 54 cold side will surge. It does not have a MWE slot, and the extra volume it is trying to push will just blast right back out the intake at times and stall the compressor.

 

I had never thought of that...that is darn good, and useful info right there!