The 98 Firebird is better, and you can put an LT-1 in it if you want to go faster later.
There are a couple of Firebirds running the 3.8, and the guy I talked to was bragging about the heads.
Jeff is correct, find someone who makes them, and have them submit one to get it approved. Same with the pistons.
You need to find a 200 Metric transmission that bolts to that block, anything else is too much and too heavy.