I was lucky to scrounge a plate that adapts TeleVue's clamshell ring mount to the old Super Polaris Mount. This plate is not made anymore in favour of a Vixen style quick release plate the SP mount never used, it lacks a quick release saddle. Only two screws hold the plate in place much like it holds the tube rings for the 102mm. Two screws underneath the plate hold the clamshell in position thus supporting the Pronto. There is little to no flex.
The quick release system is preferred, but since my mount pre-dates that era, I would have to get a saddle machined (not cheap) and an extra universal dovetail plate.
The SP mount still needs new wood legs and maybe a fresh coat of paint to bring it into the 21st century not to mention a set of new motor drives (very expensive!)
Photos are up on my Facebook profile, but I will have new photos of this rig on here later.