I wish I would've seen this a few days earlier. I know you already purchased it, but I have some suggestions and some advice for future reference.
I JUST sold my 98 WS-6 Trans Am. For reference, it had 163K miles, but it was the LS-1 motor and it was the real deal WS-6. I got $3500 for it.
I can already give you a list of problems to expect. First thing I noticed is the Auto tranny. That 4l60e tranny won't last you a long time. They are built like garbage and you'll either throw an P1887 code soon and have to do an oversized valve body kit (~$300) or he's already done it.
Your next worry is going to be the rear end on that car. Those 10 bolts hold up for a while, but after a lot of miles you may actually be looking at a new rear end which will be ~$1000.
The window motor is going to cost you an arm and a leg. The actual motor itself is only $80 at advanced auto parts with a lifetime warranty. That's the easy part. The hard part is you have to get someone who has done the motor and regulator a few times. You have to take the door panels off, drill out the rivets, drill out a large hole to reach the motor, and then start replacing everything. It's about a 4 hour labor job. That will be the part that costs you the most. Trust me I had my window motor go out 2 months ago, but I have friends that own a shop, so we did it together one night for VERY cheap.
Don't leave the car out in the sun for too long either. That dash pad has a nasty little habit of cracking in a lot of places, and a replacement dash pad is $180 from the dealer. (That would be the only place I get a new one from) Also those door panels also have a nasty habit of cracking right down the middle. Those aren't cheap to replace either.
Sorry to be such a downer, but I worked in the auction industry for 5 years and I also owned a few of these. F-Bodies can be a lot of fun, but it sounds like the guy did exactly what he wanted you to do, which is get sucked in to "A classic american muscle car". It looks clean from the pictures though, and you should have some fun with it.
Let me be clear: As long as you're happy, then that's all that really matters!
Hope you enjoy it, and if you have any questions regarding repairs, where to find stuff, or overall just general knowledge about these cars, let me know, I'll be happy to help.
