[mr48chev]

The bearing will probably have to be found by measurements although you might adapt a bearing from a a later car or truck steering column.

I think what most guys are doing is finding a bearing that fits inside the tube and around the shaft that is sealed on both sides. you will need to figure out how to hold the bearing in place in the tube but that shouldn't be too hard.
You will have to cut the shaft and tube off the gear box long enough so that you can shorten the tube so a few inches of the shaft stick out for the joint you use can slip on the shaft. Then you will either have to have the shaft cut for a key or do something so that the joint will safely stay in place and not come loose when you drive. I don't view welding as an option there. It isn't hard but there are several steps involved.