Suspension upgrade?

FIRST thing to do is evaluate what you have. Get a friend and look for any play, anywhere, WATCH as the friend moves the wheel from the column on down.

WHAT do you have for shocks, tires, T bars? Was it a slant car? Does it have at the least a factory anti-sway bar?

How about REAR springs and condition. MUCH wandering "soft" steering is due to play in the spring shackles or just weak springs.

TIRES very important, and SHOCKS

As others have said, alignment.