The sprint car rear end mounts are like what you have, and the midget mounts are what has been on the after market mount, I've seen after market mounts for the sprint car bolt pattern, but don't remember where now. Midget, sprint car, the caliper doesn't know the difference, just round up one for a midget and bolt it on. A lot of midget rears have the original mount bosses broken off, lack of maintenance on the rear end causes this, they need to be kept tight, really tight, ck out a new one sometime, and see how hard it is to roll the axle, has to be that way because the magnesium expands so much. Bob!