1 Fine 69

Hey im putting the rear end back together on my 69. I got 12 inch wilwood discbrakes all around.I go to put on the rotor over the studs and i find it wont seat properly. it doesnt slid all the way flow to the studs. I figure out its because when the threads stop on the stud and it gets flanged, its to wide so the rotor holes wont slip all the way down. Now im thinkking im gunna drill out the wholes a couple thousandths, or grind down the studs. Which should i do?

oh! while im at it i dont wanna make another thread, but how much vacuum minimum you think i need?