stance question

[gary67]

We bought a 71 truck it has a late model bed on it and 15 inch wheels. We are thinking of lowering it. The differences between front and back is 7 inches, between the top of the tire and the wheel well. we don't know if it has new springs is there any way to find out from the ground to a point on the frame
or the body what it should be or should i just start with new springs on back and go from there. also do you think the difference in the weight of the bed is a factor?

thanks
for any help.