Use a grinding wheel and cut a cross in the rivet head, avoid touching the frame. Use a cold chisel and heavy hammer and pop off the rivet heads. Use a punch and hammer the rivets thru the frame.
Screw that, find a friend with an acetylene torch.
Yeah, once you have the rivets out the bolts go in those holes.
I hope for your sake the coil buckets are all that is bad. When I restored my Ranger last year the passenger side, which was the one that really needed replaced, tore a hole in the frame when it came off.
Well, the hole was already there, taking the bucket off just made it bigger.
As for the spring, jack the truck up under the beam, get the wheel off, and then set a jack stand under the frame by the fuel filter and let the jack out. The spring will go to full droop.