I drove the car w/o a problem before I changed the springs. The u-joints are good, I had the driveshaft out when I pulled the trans to replace the front (& rear) seal.
I'll try shimming the motor mounts next, no big deal because I have to lift the engine in order to pull the oil pan & replace the dried out rear main seal (Front seal too).
I bought this El Camino because I owned a 71' when I was a kid, it was a SS454 4spd., it was my daily driver from 1973 - 1984... Stupid me, I sold it to buy the new body styled 1978.