Very long story how I got here but have R4J frame and 5K swing arm and rear caliper/holder. There is no lug to attach rear brake torque arm above the swing arm pivot on frame but there does seem to be one below. so looking for a setup to mount caliper below swing arm. Was thinking of an RS125 caliper, holder and torque arm. Is there something that will work?

Alternatively would it be easier to just get the R4J swing arm. I do have the caliper carrier that fits that swingarm, but i think the caliper itself is different but should not be hard to find. Is the 5K swingarm noticeably stronger for racetrack use with slicks?