I swapped my stock MC for a 5/8" unit from an '07 Kawasaki 600. I also put the 6-piston calipers from the Kawi onto my Sprint. I love it!
I highly recommend the 5/8" MC & 6-pot mod, but I have no clue what radial MC would be right for a Sprint. I would imagine that pretty much all of them fit, but you want to match the cylinder to the calipers you're using. BTW, I paid well under $100 for the whole setup on eBay, & the HH-rated pads were brand new.
Cheers, HTH,
-Kit
