. . . Probably gonna go with the Titan Fitness T-3 rack. Thinking 24 deep, any reason to go to 36? Height of 82, any reason to go to 91? . . .
Don't think the barbell would have enough horizontal drift during a rep to require 36" depth,
but, are you going to bolt it down? If not, and you slam a heavy squat back into the J-hooks, the rack might(?) wanna tilt a little. The deeper the footprint the better in that case.
If you (and your son?) can do pullups from an 82" bar without too much foot drag, maybe 91" is a waste of money? Might make a difference if someone too tall wanted to do overhead presses while standing rather than seated?