Do you have the caliper piston retracted all the way back into the bore of the caliper?
I have had your problem a time or two in the past when both replacing rotors and pads at the same time, with new.
But nothing that sanding down the new pads a bit didn't take care of.
Sometimes manufactures tolerances aren't the greatest anymore, when your trying to fit new parts together at the same time.
Where did you get the rotors?
Rotors for the 70-72 B & E body cars aren't the easiest things to come across these days.
Unless you got the wrong parts, or mix boxed parts, your now screwed, as you already machined the new rotors that you just installed.
You won't be able to return them, if they are indeed the improper ones.
The only other thing that i can think of, is the bearing race in the hub of the rotor, isn't seated all the way down, or that area in the rotor was machined wrong from the git go.
Anyway, good luck in getting it figured out.
Jim V.