Gt 2

You can find a lot on this board by using the search feature. Big issues on GT2 is providing body supports on the rear half to avoid the infamous "butt sagg" and protecting the windshield with your life as they are a specialty item that are getting very rare and expensive. Jeff Troy will sell you a CD that has a digital version of the original manual, etc. His CD on the GT2 is not as "rich" with information as the one for the original GT because he included pictures and other documentation of his building and rebuilding the GT, but it has at least all that the original purchasers of the GT2 kits had available to them.
Warmest Regards...

"Best parts" needs some clarification. Best engine parts? Best chassis parts, best what?

And by best do you mean price is no object best, or where is the best place to get good parts?

Interior parts are likely to be custom made. You can make a patetrn and do them yourself or bring it to a shop. On rare occasions interior packages do pop up but they can be few and far between. Unless you try to be creative the interior can be very expensive.