Just a thought ,it wouldn't be that hard to make a pair of hubs and bolt a pair of smaller calipers one top and bottom .The only small problem would be bleeding the bottom one .You would have to take it off to bleed so the bleeer is pointing up with something between the brake pads.This would be a cheaper way to to go if have a lathe and your a good fabricator
Just a thought Paul

1948 Chevy 2 ton flatbed ex fire truck , and various motorcycles .