67 mustang with borgeson style steering box

Might be worth a call to Borgeson's tech line.

@67coupestang Did you resolve this issue? The wheels on the pavement decide whether or not they are going to return to center or not. Stock non power steering cars were adjusted to '0' caster, so that the vehicle could be steered. Anything power needs to be adjusted to 5 or 6 +caster so that the setup will return to center. If you were to try to steer a power steering adjusted to 5 to 7 +caster without the power on, it would be very difficult to steer but it would return to center.
I just reread your original thread. Hopefully you will be able to get the Borgeson box adjusted back like it should be without having to remove it to send to them to readjust it. You don't want it locking up on you.
?? What ps pump are you using?
ADDED: Also, how old are your upper and lower control arms. After owning dozens of these old mustangs, I've seen about every abnormal condition.
If your ball joints are old and freezing up, that could cause a lot of issues. They should freely swivel in their sockets.