I'm no expert, mostly I follow the board. fmartin and others have done this swap. I'm sure they will correct me if I get it wrong but my imperfect understanding is:
To do the T-5 swap you will need a 3-speed bell housing to modify. John Mummert? at the Y-block site will do it on an exchange basis plus he has the other parts and can direct you to the right source for the proper trans.
Over on the HAMB there have been some that said the GM Saginaw 3 or 4 speed is easily? adapted to the 4-speed bell.
I have no idea about autos other than the Ford-O-Matic that came stock behind some 223s, old tech but rugged and dependable.
All that being said, whats wrong with your 4-speed? Forth gear is 1:1 same as most trans (non-overdrive). I drive one in Phoenix and its not that bad. I would think that with the torque from a 262 it would be even better. As for highway, I'm changing out the rear diff to 3.50 gears. I have found several "pumpkins" for around a hundred bucks.
I hope this helps.
Dave