I'd love to put a set of PM rear calipers on this bike, but I don't have an extra six-hundred bucks laying around. Screwing around in the shop last night with a set of stock XL calipers and they seemed to nestle into the frame nicely. The stock Sportster caliper uses the swingarm as an anchor. Considering tacking a piece of 1 1/2" channel to the inside of the bottom tail section of the frame. I'll need a shorter axle adjuster as well.
Love to hear from anyone who's done this or something similar and can enlighten me.