OK, seems like I'm on my own here. No reason to maintain this thread as I will be largely talking to myself. I plan to try to get the motor to run with what I have and take it from there.
You're right, this is an old thread. I just now stumbled across it and although I don't know much about Square Fours, I immediately thought of Pierce Manifold up in Hollister, CA. They are our go to source for odd Weber parts and they also stock some Solex parts. Their website only shows Solex carb kits but it is still probably worth giving them a call. Be ready with some physical dimensions, thread size and pitch and what size orofice you want. I've always found them helpful and knowledgeable. And if they can't help, they may know someone who can.https://www.piercemanifolds.com/default.asp