OK so i have a '"stock" 1991 Firebird Formula with (supposely) the L98. However, when I bought the car, the previous owner said that he had blown the original engine and transplanted an engine from a 95 trans am. i didnt know much about the different engines at that time and now i am not sure what I have. I have the stock tpi setup still under the hood but i am not sure on the block. Is it possible to run an lt1 under the tpi setup from the thirdgens? also if this is the original, it has many many miles on it and I am looking forward to swaping the engine out when i get the cash.
Here are my options:

1. ZZ4
2. LS1

What am looking for is an engine dependable and easily tuned. The goal i want for this is to get as close to 500hp as possible. I am looking for some advice in what direction to go.

I know it is a lot to read thanks for sticking with it.