You can run that box. But it has a ratio of 16:1, the manual box has a ratio of 19:1. It will be harder to turn at low speeds. I have done that in the past,. It was only a problem when parallel parking IMHO.
probably not; i had my 68 base, 289, 3 spd. stick MT swapped with PS from a 67 falcon(Ebay); think the center link was different, though mechanic went from tie rod to tie rod across. It came with a pump, reservoir, pulley, and rack and pinion, whole thing for $130! I did it because when turning for parking\ or backing up it was awful. I saved the manual piece in case somebody wanted to revert back to original. PS is deadly quick responsive, especially if in the 69 351; '68 390's or to the discriminating, 427 probably had MT. Good luck.