Rear coils to leafs frame ?

[1-PU70]

Is the frame for rear coils the same as the frame for rear leafs? I have a 70 with rear coils and It dont quite cut it when its loaded and towing. It has HD coils, shocks with coils on them and the factory overload spring. According to the NAPA web site the HD rear coils are rated at 2900lbs each. If I went to leafs I could go to 3500lb springs and then add a top helper rated at 1050. I know the coils ride way better then the leafs and I hate to give up my coil ride. If you have any other ideas just pipe in. Thanks. Oh ya no air ride. Dont want to spend the coin. The only other idea was to get the air bags that go inside the coils but i wanted something that was real simple.