I had my steering box rebuilt by "RedHead Gears". They install precision roller needle-bearings where there were none from the factory, and tighten up the whole affair remarkably.
I also had a custom ratio put in mine.
My 79 Z28 has an incredibly quick steering ratio, makes the car an absolute blast to drive. The stock mach 1 steering box is dreadfully slow in comparison. Seems like you are always turning the wheel!
I had the Mustang box rebuilt with the ratio that the Camaro has and wow!...what an amzing difference!
It makes the Mustang far more pleasurable to drive, I recommend it.
The Borgeson Saganaw steering boxes have SPA identifiers. I believe the "T" box is the variable ratio but i am not positive and cannot see clearly from the pics. A quick call to Lee Manufacturing folks shold shed some light on which unit you have.