I measured the rolled pipe on my 49 and its 1 3/4 od.
I was wondering why he used 1 1/4 pipe
1-1/4 pipe is 1.66 OD, which is closest to 1-3/4 if you're using steel pipe and not steel tubing, which is sized on OD. 1-1/2 inch is 1.9 OD, which would be significantly larger (and heavier) than the desired 1-3/4 size.