my car was cracked here as well. and it had air shocks when i got it.4 leafs are fine unless you have passengers in the rear seat then you may find your tail draging ,one thing i would not recamend is air shocks or heavy duty coilover shocks they are to much for the rear crossmenber and cause it to crack across the shock access holes from the floor flexing if the shocks wont give something else has to
i have worked on several cars that had air shocks at one time and the floors are always cracked there
yea when you air those shocks up you take the weight off the leafs and place it on the rear cross member and shocks. i have seen the shocks punch through the brace , this was a pretty common thing to do in the good old days ,me included,the coil overs were just as bad . i still see people do this, bad idea.set the springs up right in the first place its a lot cheaper in the long run, the 4 leaf with a half leaf in the front is probably the beter way to go not as stiff and the front leaf helps stop wrap up and if you still get wheel hop add traction barsmy car was cracked here as well. and it had air shocks when i got it.