Just had a look in my workshop, and I think I have one! The hole centres are 3 1/4" at the top and 2 1/4" at the bottom, I thought there might be a casting number, but no. You can try PM ing me, but I'm too tight to pay for the privelige of extra PM's. I do post on the RAT forum as well as Mick Barratt, funnily enough, my name, PM works on there!
Thanks, just checked though, the stud centres on the top are 4" and 2" on the bottom. I don't know what machine that one you have is off, must be small, 350cc maybe ? 3T ?
I did come across one in California on ebay and am waiting for the seller to tell me the part number on it, cannot make it out with my eyesight.