Rounded or squared, I'm not so sure that is the game changer, I have a 1969 vintage Comp + in the box (new and complete) and the handle is the rounded type, but uses two bolts to fasten to the shifter. No GM part number.
I wasn't meaning for that to sound like a " game changer". I also stated that originals slipped in & locked . I'm merely asking general questions about the shifter in question..