Another option. I had a homemade rear weight set on one of my 641's. Just take a small piece of big steel pipe. weld it to the disc, weld a few pieces of rebar like at 12/3/6/9 o'clock and one as a round ring, put a sona tube over it, and pour concrete. Not the prettiest but works. I don't see why you couldn't do this on a front rim.