Doctor Diff- manufacturer seems to depend on the ratio and carrier. Not sure of the country of origin on some of them, some (like the 3.55/741) seem to be his own brand. Could always ask him. Not a bad price, either.
I bought a set of 3.55s from Cass 18 months ago and the invoice was marked Motive/Richmond but when they arrived they were in the styrofoam but the outer cardboard box was missing? Hmmm...
I'm breaking them in now, but have no complaints so far. I'm going from 2.76 gears to 3.55 BIG difference.