I tried something similar a couple of years ago when we needed to replace one of the elevators on our RV4. We didn't have any luck finding any pre-made parts so in the end found a local(ish) builder/inspector who made the new elevator for us from Vans supplied parts. As you mentioned already given that RV4's are not match drilled kits like most of the more recent kits, you'll inevitably find that parts are unlikely to fit if already drilled etc. There are lots of experienced builders around so it might be worth seeing if anyone if willing to help make the parts you need.