7 1/4 Vs 8 1/4

I think you should be OK?

It all boils down to your rim offset. When they started using the 8 1/4 on the later years the cars had not only larger rear 1.4s for bigger tires, but the axles were narrowed a bit. I think you will be OK.

Can you set it up on the springs and do a mock up with your tires.