That seems like an awfully big combo to get under the fender. I don't know the 71-73s that well but you also have a '70 and if you compare the clearance room of both that will help. I have a '70 with stock rear springs and 1" lowered front. I run 295/50R15s in back and 235/60R15s in front. I have plenty of room up front so there is some room for larger rubber but you need to compare the overall height/width since you're running larger diameter wheels. In back, my fender lips are rolled and I think I would rub with stock lips so you need to have a smaller overall combo that that, depending upon the differences between '70 and '71 wells.