I am also going to make my own seats. After I got a ride in my friend's RV-7A with still-in-the-plastic Oregon Aero seat cushions I was more convinced than ever. So before Howard sent the cushions off to be upholstered, I went back with a big set of calipers and took some "starting" measurements since I'm 6' 5" and my wife is 5' 0". Here's a couple of pics and the source I used here in the U.S.
Tom's Web Page
The measurements are out in the garage. If you want, send me an email
Tom , I'll scan the page and send the image to you.
Cheers,
Tom