It comes with the carrier bearing as one unit and is not replaceable all by itself. Timken manufactures the carrier bearings. Most auto parts stores carry them. Easy to change out and inexpensive. The only hard part can be getting the old one off the driveshaft. When you first look at it, you'll think that you can slide the old carrier bearing off the front driveshaft when under the truck by simply sliding it off. Maybe you'll get lucky, but you'll probably have to remove the front driveshaft so that you can put in in a bench vice to carefully cut the bearing off using an angle grinder and a Dremel. When the cut starts to get close to the driveshaft, stop and finish it with a cold chisel. The cold chisel acts like a wedge when you drive it into the cut and it will snap the remaining metal to release the carrier bearing from the driveshaft. The new carrier bearing slides right on. Careful for the rounded collar that is in front of the bearing. It is attached to the driveshaft and is not part of the carrier bearing. so be careful working around it.
When I had to replace the bearing in my center carrier, I managed to save the rubber cushion and only replace the bearing, which was available from my local parts store. They also had a center carrier complete, new bearing, new rubber, new hanger, which was actually cheaper than the bearing itself. I got the bearing because I wanted to maintain as much originality as possible. The new carrier had a shorter hanger than the original, and would have required spacers to get to the correct height.
For me the hardest part was removing the yoke so I could get things apart. There was no way to get the cotter out of the castellated nut, so I ended up cutting the nut with a cold chisel! Once that was done, it went easily.
Mine is a 1 ton, but I would assume the same would work for a 3/4 ton. It seems they used that bearing for years (at least up into the 70's).
Tim
I am currently digging back in to a 1953 3800 (one ton) with a nine foot bed. I've owned it since 1979, and drove it until 1982 (or so). My wife got me involved in restoring it back in 2002, got the body removed and the frame redone, then things came up. Now I am retired and starting again. If anyone is interested I have photos on Imagur ( https://timwhiteblues.imgur.com/ ). I live way back in the woods in the Ozarks on 40 acres at the end of a 2 1/2 mile private road.