Trying to figure out the wheel size I need to order.

What’s the actual width of the B-body rear axle?

They’re not all the same, they actually vary by a couple inches depending on the model year.

That said, even the “short” one may be tough to find a 15x7 for with enough backspace to fit on an early A.

What point to what point is the measurement taken?

Right now I'm thinking that a 15 x 7 with a 5.5" backspace may get me there and I have found a few of them. Hate spending $400-500 and being wrong.