
My idea at the moment, as I’m pretty sure at least one of my mounts has shifted, is a floor standing bracket bolted onto the outer face of the swing arm, and then positioning the mount off the swing arm. The inner swing arm mounts are of course Ok. So I’d get the swing arm face vertical, and lined up for and aft (possibly using a looong thing stuck to it extending forward), and tack the mount in position onto the chassis. I don’t recall seeing it done on any threads currently or in the past.
At present my swing arm mounts are patched on in a bodge to get it through the MOT last summer. Looks horrible but it stopped the clonk as the mount shifted under acceleration and cornering. My wheels are well squint. I thought no my MOT man must have a soft spot for me...