I looked at the Proctor offerings, but when you compare them to a full-scale turnbuckle there are a lot of issues. The Kavan ones I hadn't seen but they're closer. From what I could eyeball on my trip to see an in-the-bones Pup in San Diego, there are about 4 basic types (lengths and rod ends) and the Kavan offering would be OK for one of those types. They look very nice though!

I think the biggest ones were almost a foot long including the ends, so half scale would be something like 6 inches! The internal turnbuckles were closer to 4 inches, so 1 1/2 would probably be ok but most people would never see those anyway. The major issue is how to machine the eyes, thimbles, and shackles. I think once I get the basics figured out I can go back to the Air and Space Museum and see if I can make better scale drawings.

Steve