If you want a scratchbuilt shuttle 1/72 or larger, you could use the plans by Luther Hux for a 1/72 orbiter or the later 1/48 one that he did. Although even at that, his were built a bit overkill. Long ago, a local R/C Club had a 1/48 model based on his plans, but they built it like a tank, as though it was a pattern plane with a .60 or bigger engine, rather than build it like a glider. Heavy balsa too, no contest grade wood. It glided like a rock and landed at a scale speed of about Mach-2 or more. When I asked about it, they said "the real thing" glides like a rock. I wished SO MUCH I could have flown my R/C orbiter at that same event so they could have seen that if you expect a rock and build a rock.... you GET a rock. But if you expect a glider and build like a glider.... you get a glider. Not a GREAT glider, but night and day difference. But as it was, I don't think there were any sailplane pilots in that club.... at least not anyone who would admit it.
Anyway.....
If you did 1/72, then you could use the Monogram/Revell shuttle for some master parts to vac-form (My site has info on how to make up an easy DIY Vacuform).
But since you mentioned the Guillows orbiter,s I hope that is more towards what you are looking to do. Much easier. My first-ever shuttle stack was a scratchbuilt 1/110 model, in 1979. A few years ago, I made another one at 1/110, which was a prototype for a kit I was planning at one point to do (didn't happen). Anyway, it worked great with the Guillows orbiter. I never did get around to trying to paint the orbiter, to save weight I was going to do black magic marker for most of the coloring and some decals or printed adhesive paper for certain areas like the cockpit and markings. The SRB's were going to have adhesive paper wraps with SRB details/markings printed onto them.
Here is a link to the thread where I discussed that model, when it was still going to be a kit.
https://www.rocketryforum.com/showthread.php?8053-1-110-Scale-Shuttle-model-is-a-success!
And a photo below of the prototype, as far as it got. The orbiter had cockpit and markings printed onto normal paper and taped on, as I was not ready yet to justify buying the 14" long 50-pack of adhesive paper the kit would have used.
- George Gassaway