they're primo calipers, I'd snap them up at that price, adapter brackets are no big deal to get made up by a machinist, and it's not rocket science to make your own at home with hacksaw, drill and ruler but the mating surfaces have to be perfectly flat .
Mine bolted direct to swapped-in 41mm FZR forks with 320mm discs, got the bluespots US ebay dirt-cheap, something like 30 bucks, they seem heaps dearer these days though, work best with 14mm cylinder where you get a soft progressive feel with thunderous power hovering at the tip of just one finger.
The XS11 37mm forks will get whippy if you squeeze the lever hard but hey who tries stoppies on a 600lb XS11 anyway.
The bluespots are easy enough to strip completely, they're compact and one-piece unlike lots of other 4-pot calipers that split in two halves. To get the pistons out use a suitable sized piece of thin board which allows you to hold two pistons in whilst you use a simple tyre foot-pump to squeeze the opposing pair out.
Takes a bit of juggling between each side. The anodized blue alloy "spots" you don't need to buy the special tool to remove them because it's not necessary to do so. A flexy feeler-gauge blade is good for digging the rubber seals out of the cylinders to check for corrosion and gunk in the grooves
ps check this chaindrive bike doing some hillclimbs and stuff. youtube XS1100 onboard
