I remember richrs2k and think I've seen the car, thou cannot be sure!

The MTX-75 box is pretty strong, but not industructable! So might be wise to remove it and give it a good inspection

As you have suspected the usual cause of the car veering left and right on the throttle is the lower arms, but since you have replaced these it has to be engine mounts or the gearbox itself. The inner CV joints, also known as tripods, can wear and are quite expensive from Fords, so a quick solution is to swap them over as they wear in 1 direction by swapping them you are then wearing them in a fresh direction