I am putting an engine on a mountain bike frame as well, and one thing I noticed is that my frame is similar to yours in that the front tube where the engine mounts is not round but oval shaped. Did you have to install longer studs in the block to fit around this tube, or were the ones provides sufficient?
I had to get threaded rod from the hardware and cut it long enough then thread it in,I tapped mine out to standard threads as I could not find any metric rod,I had the big mount engine,So I wrapped rubber around my frame before I put the engine on.I have now ordered a huffy cranbrook to put my motor on for a tighter fit.
