Here is the thing with 1st gen cars.
1st off is it an X car? X11's and X22's are worth more than other vins.
2nd is going to be is it a "tuner" car or a restoration. Obviously this is a tuner car so now it changes the value.
I have seen some really nice tuner cars and most of the really well done LSX 1st gens (im talking mirrors under the car and you can eat off the bottom of the car) have been going for 30-45k complete.
I don't know where you are in your car yet; however, that is what I want to build at some point (or buy complete). I have the opportunity to buy a completely restored and all factory origional 67 RS car with low miles for $23,500 locally. I haven't done it because I want to put an LSX in the car and cannot see doing that to the origional numbers matching car.
I had a friend sell a 69 X car recently for only 10k! I wish he had called me cause I would have bought it, but this was a solid car no rust good paint and with a 454 built just needing motor assembly and installation.
It really sucks, but unless the car is complete and flawless you are going to be pushing it to get over $25k and incomplete you won't see more than maybe $15k if you find that perfect buyer. This is all pending that it is a desirable vin.
Good luck on your project, I envy you being able to spend that kind of money and time on such a wonderful car and a great piece of American Heritage. 1st Gen Tuner cars are AWESOME completed. I have considered and wanted one for some time now. I have toyed with the idea of ordering a Foose Resto Tuner car for about a year now.
Good luck and Post some pics!