A few good things to check, but a few are already good. The X-member is level and centered in the frame at ride height, the lower control arms are level. I did check the strut brackets, but will re-check centerline and look for cracks.
Can't imagine the centerline being off since I did not modify the struts at all from the original '74, just made the brackets to fit the original geometry.
I'd say these problems are fairly new, but always existed to a lesser degree. The car was aligned last in 1977, and that was not a high quality shop. My most recent change was to the 205/55 R15s from 195/70 R14s which took away a lot of rubber height, and lowered the tire profile a good bit. The 15 inch wheels have about an inch more of offset than the 14s did, so I might be trying to drive a "ricer" without even knowing it. I'll check some fellow rodders here in Phoenix and see if there is anybody still alive who knows how to align a '74 Mustang II.
I appreciate your response.