Like TurboDomestics said,
www.starquestclub.com is an amazing resource. You can learn almost anything and everything you want to know about the car there after some digging.
Aim for 88/89 years. Stronger tranny, rear end, better suspension (SHP Option), and other misc. changes. 87 is OK, but if you go any earlier you'll be looking at bigger issues that are harder to get around to make power. Pre 85.5 aren't intercooled, and the pre 86's have a different computer. 87 to 88/89 is easy to swap parts, but the older years aren't quite so compliant.
Of course if you're going to do an engine swap, it's a bit different. However, i'm in the minority - I actually support the G54B. If you like torque, you'll like this engine. If you get one, just keep in mind it is NOT a 4G63. You won't see the same results - it's a whole new game. MPI is readily availible for the car if you can't stand TBI, and DOHC is on the way.
Don't pay more than a couple grand unless the thing is SERIOUSLLY modded or MINT as hell.
Oh yeah, and my quest will be for sale shortly. I won't advertise it here, but if you're interested PM me.