My rod has a great ride, until you hit a bump or rut in the road.
Smooth quiet ride on good roads, sounds terrible when you hit a bump.
It has leaf springs and new shocks. Would those helper springs on the shocks help? never used them before.

Are the leafs stock ?

yes, they are factory. To be honest I feel pretty sure they were checked out when the car was being built.

I did remove a leaf a couple of years ago because the car sat too high. This thing had 10 leafs in each spring.

I would check for for a broken leaf? after 70 years of movement the springs are now flexing more or a bushing may be binding ? Thats where i would start.
I have a 37 dodge 4door and im gonna use toyota pu leaf assembly. any minitruck springs will work and can be bought cheap. And is an easy way to update your suspension

Is your problem a suspension problem, or a body to frame or fenders to body issue? Lots of stuff to go different directions then come back together after a bump back there. Gene

I will get it on a rack and chek things out , again. Some good points ,thanks.