Brand new Centric drums don't fit?

Anyone heard that the new Centric SBP brake drums "lock up" the rear end when tightened down? I was talking with a gent on the FB "Early Valiant and Barracuda "page. He has a problem of new Centric SBP brake drums "locking against the backing plate when tightened down" on his '65 Barracuda's 7.25 rear end. Apparently, he's tried several sets, with the same result. He says the rear end is totally stock.

Anyone heard of this?