I need advice on rear coil sprins

[KevC20]

I am redoing the suspension on my 71 Cheyenne LB c/20(sb 350) and went to rock auto to buy rear coil springs. There are several to choose from, constant ,variable pitch, professional... and then standard or heavy duty. Not sure what is stock for this truck.

I looked under the truck and it doesn't look like they are "variable" as the springs look evenly spaced. There is about 5 or 6 coils. This truck did come with the "auxiliary" leaf but it is not installed.

Any advise would be greatly appreciated.
Going to watch the game --roll tide!