Lincoln Enterprises didn't have a whole lot as far as resources go. Maybe copies of the same layouts that were in TMoST and some Mike McMaster blueprint sets and posters. Beyond that, we're talking grainy promotional stills and the AMT model available at the time.
I know there were a few other odds and ends from the series that made it to the book (this was after the first run of blueprints sold, remember), but I have no idea what was left of that. I -think- he got some shots of the set mini as well, which is what a lot of the diagrams was based on.
Either way, though, it's absolutely amazing what he was able to accomplish, by hand, with what resources he DID have available.