International Trucks. Who's got um

As dialiant said , if you swap you have to change everything. I'm more for trying to keep it the way it is if the parts work. I would like to swap out the non syncro 4speed. Parts are around , I have a cousin who's family has own the international Harvester truck and tractor in Okanogan Wa for the last 60 yes. He can probably source me some of the things I need and tell me what will work or not.