big or little u-joint?

There is a considerable increase in strength, it even matters if the are cross drilled to make them greasable. Does your rear end already have the larger yoke for the bigger u- joint? I would get a bigger yoke and u- joint for the 727 to match the larger rear joint if it were me. Why leave a weak link in the drive line, especially in the front. That's the end that if it breaks, can pole vault you into the air....