fullcameron; if the top triple clamp has fork tube clamp bolts then the whole front end was changed, I'm sure we can guess why. I see "frontend-ectomy" fairly often on used bikes. The 72 RH leg is also a one year deal, with a larger axle hole to fit threaded collar # 27 in the diagram above and lock nut that helps locate the disk rotor.
My 73 215563 born on date 2-73 has the 6 bolt rotor.
My 73 215563 born on date 2-73 has the 6 bolt rotor.