Standard 540 PTO is 1 3/8 diameter and I believe 6 teeth so does not sound like a 540 PTO. Are there any pictures of the female spline end on the tiller PTO shaft? Should look same as the rear PTO on your BX.I believe it is 540 but maybe the shaft itself is smaller, I don't know. The post said "3/4"inch splined PTO shaft".