swap tranny

I have a 350 SBC in a '73 FJ55 mated to original T-case (I believe) and original 3-speed tranny (with various adaptors and cross-members, etc). Speedo and e-brake are already gone (and I'd like to get back/working). I want to go 5-speed manual 4x4...not for offroading/crawling but to do...

is any one mod the tranny to 5 or 6 speed? i wonder if the housing are matched with 4.7 engine? or information on how to swap. thanks