Here's a little something I whipped up this evening. This is a fake Momo I purchased off ebay for $55. It's 345mm diameter, 70mm mounting holes. The rim is actually pretty nice for a knock off, though I don't think I'd use it in a real car. However, on a sim wheel, it's great. The suede feels nice.
The adapter is CNC machined from a piece of HDPE I had laying around. It mounts nice and snug despite being a piece of plastic and having been a simple prototype:
So still some more room for improvement. This was just a proof of concept. I raced with it for a little while and being seated in F1 position the rim is a bit on the large side... The paddles are also a bit of a reach with a rim this large.
Anyhow, pretty cool