[FWB]

most are replacing everything because they were from a donor car, 1978 is a long time to expect bushings to still be good. so if your replacing the upper because the upper shaft bushings and bj are toast then the lower arm will be suffering from the same fate. i put the heidt's tubular arms on mine. i opted to change the lower to their arm that accepts coil over shocks. with that i upgraded the small brakes to 11" and wilwood calipers. it made a huge difference in the car. the stamped steel ones are ok but will still flex under load, the tubular type is stronger and lighter, you can mix them with what you have and replace the others as you go. but i would do the same to both sides with whatever choice you make