I never had a real problem or need for a right side petcock. On my original 1982 tank, as far as riding, it was easy to slosh the fuel from the right side to the left side when needed (i.e., left side empty and still looking for a gas station). Full drainage was never a problem, I just took the tank off, tilted it as needed, and drained it.
My current tank (used R65 replacement from unknown year model) does not even hold fuel on the right side of the "hump." Although the tank looks normal from the exterior, the tank interior is blocked off on the right side of the hump.