Wild & KZ Guy --
You should start a new thread for this, since it's a different topic.
I'm not sure about the manual-type petcock, but I recently installed a vacuum-type Suzuki petcock I bought from Z1 on my SR with no machining required. Giftofthegods77 had success doing the same on his '79 SR.
See
my recent thread
on the topic if you're interested in replacing a vacuum-type petcock without having to convert to manual operation.