I got the leather for my current project from Kyson leather out of North Carolina. They are very reasonable and have a very wide selection of hides in any color you want. They are on ebay and will send you samples of any hide. There is special thread for open car interiors that will inhibit UV rot. Almost all early open cars had leather upholstry because they were exposed to the elements. I think I paid around $125 per hide and they were huge, almost eight feet by seven feet. There is some wasteof course. Hope this helps.
I'll cast my vote for the near leather or ultra leather. it will stand up way better in an open car and is what I'll use in my 26 RPU.
Your roadster is a stunner! As good as it gets! I'd love to see more shots, if you have an album link. Mike