rear disc dia / piston dia?

Hey, does anyone have the rear caliper dia and the effective radius (centerline of axle to centerline of piston distance) handy?
specifically for a 2004 zr2 blazer, but i think all disc s10/blazer rears have basically the same setup?

just wanting to run some quick math for potential hydraulic parking brake mods

Wanting a hand brake for ice racing? 

I don't think I have any rear calipers left in the barn. I'm pretty sure I rage quit them after finding the Blazer's locked up last year, but if you shoot me a reminder text during the day tomorrow I'll poke around the axles in the field.