steering help

once i did the upper A-ARM drop and manual steering adapter mine stop doing that.

First, welcome to the forum... As for your symptoms, its a common complaint. Most folks have been able to minimize (if not completely eliminate) the problem by completely rebuilding the suspension and steering components and making sure everything is adjusted correctly (like the steering box).

Since it appears you've done most of that stuff, I can only suggest actually getting under the car and taking a look to see where the play is. Start by crawling under the car and try moving parts of the steering with your hands. Look at the idler arm and pitman arm mounts, play in the tie rod ends, etc. If anything is easily moved or shows play, fix it.

If that goes well, have someone start the car and turn the wheel while you look for play in the power steering system. Notice how much travel there is at the steering wheel before the steering box moves, and how much the steering box moves before the steering system actually moves. I know you mentioned you adjusted the steering box a bit, but perhaps it needs more.

of note: adjusting the steering box is fine, but if the box is 35 years old, a replacement may be in order. If your ball joints, tie rods, center link and bushings are new or in very good condition, then you may have to consider replacing the steering box. You can purchase a Flaming River box for your Stang with a 16:1 ratio. That will give you tighter steering and a quicker reaction time.