Tranny swap

Hey guys, i'm looking into swapping my 3 speed manual tranny, as i have torn 3 teeth off of 1st and reverse, and i'm considering putting in a 4 or 5 speed. i have a 225 slant 6 and i was wondering if anyone could tell me how to do a t-5 tranny swap or if there is any kind of tranny that will just bolt right up to the bellhousing in the slant 6. Thanks a bunch