The 70 I bought for my daughter & me was hi miles and the suspension and power steering were both shot. After some research, used Canadian Mustang complete kit (got heavy rate 1" lower springs F & R) incl their Midolyne bushings. They are firmer than OEM and don't go soft over time, but do not transmit harsh road shock like poly. Now the car rides firmly but not harsh over bumps and really handles well. I totally rebuilt or replaced all PS components, incl having the box rebuilt, but you're not going to totally get rid of wander or esp. bump steer with that type of a system. The way to really fix it is to go with a rack & pinion like from
www.totalcontrol.com, but not totally cheap, either.