Hey Travis, I think the tank is from a BSA D13, I would have to dig out the paper work to be 100% sure. I would sell it, but I think the postage would be pretty expensive from the UK. PM me if you are interested.
Jack, I double checked the tyres and they are K82's not K70's. They were £55 (~$85) each fitted which I think is an ok price here in the UK, not sure about in US.
I know this is an old thread, but did you fit risers to the standard rs125 yoke? Did you bolt them or weld them? Also, i don't suppose anyone has the dimensions of the RS125 wheel spindle do they? I have loads knocking about at home, or could get one made up, trying to do it all on the cheap, and don't really want to buy one if i can help it.
why not use a GPS speedo? just needs switched live.
won't work indoors but then who needs that (unless you are an MOT shop)
Get them from aliexpress for £55