Sorry to burst your bubble, but nearly everybody selling used parts thinks he has a gem in his hands. Of course, there's always the one fool who will overpay, but assuming you don't find him...
1.You've got a 42k mile Gt - that's 20k miles /year. That means it's a daily driver and you drive a lot.
2.You've got a 2700 converter which means you rev it a lot even when you don't want to. Those 42k miles must have been pretty rough.
3.Based on the mods, you must drive hard. See #2
4.Nitrous doesn't exactly bring the value up, at least if I were the buyer. Why would anybody want a used nitrous motor?
5. The warranty, if it still would have existed, will not exist anymore.
6. You've drag raced the car...enough said.
If I were looking at your car, I wouldn't pay a penny more than $13k-14k.
Here's my advice...you can either listen or tell me to go f$%* myself. Either way it doesn't bother me...you opened yourself up to critisicm with this post:
If you're going to spend a ridiculous amount of money modifying a car, you have to either be so in love with the car that you plan on keeping it for a long long time, or you do it wisely so you can get a good amount of your investment back once you sell it.
Would you spend $100k fixing up a house just to make yourself happy if you're going to sell it in 2 years and not get back anything close to that amount? And would you fix it up in a certain way where you limit the number of potential buyers because you altered it so much?
So, just to remind you that I've answered your question, I think it's worth $13k-$14k. I hope you get more though.