I had a 74 4X4 short box 318 stick with an 8 3/4 with a 3.55 sure grip in it a few years ago and it was the big bolt pattern. I was told it was called a heavy half ton with the larger bolt. It was all factory as I had the invoice.

416 stroker from Nick at Compu-flow. 11.14 in full street trim. Seems like a new best every time out.
11.06 open headers----so far!!