RE: Venturi for 061 Wasp
I don't think they exist. I've always tied the carb wide open, but you could make your own venturi by picking up a nylon standoff at the hardware store, then final shape it while it's chucked into a drill press, or even just a drill motor clamped in a bench vise. Nylon can be worked with knife blades as a cutting tool.
I've also done aluminum venturis in a drill press, using a screwdriver as a cutting tool and the table rest as a place to steady the tool.