NEED TRANS FOR CHYEVY 350 ENGINE

I have a cousin that recently purchased a Jeep cj-5 later 70's I believe. The original engine has been swapped out with a chevy 350. The trans is a 4 spd manual but I don't know what model it is nor do I know the t-case the vehicle is equipped with.
While towing the vehicle it somehow shifted into gear and destroyed the trans. The trans has a crack from the bell housing straight down the center.
What information do I need in order to find out what trans I can swap in its place? Do I need to find the t-case model #? If so how? Do I need the bolt pattern? Can I install a 5sp trans in its place so it is better at highway speeds?
Any help would be greatly appreciated.

If it is a Chevy trans. it is either a SM420 or a SM465, these are direct swaps to the chevy bell housing and adaptable to the dana 20 transfer case.