Cragars and sizes

I have a pair of double drilled 8.5x15 centerlines on the back of my b-body, with 10.5x28 slicks. I seriously doubt that the tires will fit on my 67 notch with 7 1/4, but with the pair of 9x28 et streets i have, i think i could get them to fit.
Once i put the 8 3/4 in, might be a different story.