They probably used the same Vellum paper we used back in the 70s and 80s. With the high quality scanners that have been around for years, it amazes me that someone still makes the blueprint machines (That brings me back, I can still smell the ammonia!).
I think yours is the first build thread I've seen with someone fitting a body from Bill Hough. Since I'm about to reach that point myself, I've been following your progress with great interest.
I have a Mustang II style rack. The thread for the inner tie rod end is M14 x 1.50 and the tie rods have a 9/16-18 thread on the outer tie rod end. This looks typical for all the Mustang II style racks I've looked at. The C4 Corvette is M14 x 1.50; it looks close to a 9/16-18 but it's not...
It looks like a Mustang rack. Does Summit have tie rod ends for it that will fit the Corvette uprights? I'm facing the same challenge myself. I'm using C4 Corvette front uprights and most of the aftermarket racks are set up for Ford tie rods.