If you're sure that the trans will bolt to the block, you should be ok. I can't recall what the setup is like in the 88+ model trucks, but I found out that my 86 frame brackets (V6) would not allow the Gen III motor to bolt in. As long as you don't have that issue, good luck.

Here's a shot of the V8 brackets for my style truck that I found at a salvage yard. They allowed for the engine to mount forward by approximately 4". Again, this is for the body-style prior to yours. Better to check than do what I did by trial and error.

V8 brackets mocked in place:


V6 mounting location:


V8 mounting location: