Bassman, I had THE Walt Dupont rebuild my 59AB, the drake pumps I had were off a 1/2 hole to bolt on the block. We shipped my originals to skip and a week later they were back!!
I've since returned the drake pumps, when I find a decent orig. pair of pumps I will send those out for a future motor. Listening to folk's on the barn, not much beat the original part. Drake has fixed the prob. W/the pumps. They were great to deal with!!