Leave the bearings at the hobby shop! If you plan on useing the truck in water elements. Have a truck that I use for keeping my walks clean.Well half way through the season,the truck sat for two weeks because there was no snow.Came time to use it again & it wouldn't move!
Turns out that the axle bearings had rusted up tight.
Never used a bearing again in my drive lines.
If you want to see something kool,take one of the tamiya bushings & heat it with a torche.You won't believe how much oil will come out of them. The bushings are self lubricating.As they get hot they release oil.
That's why they last so long.
As for the trany,Claus is correct.If you install a bearing under the 2-3 shift hub,it's just a matter of time & it can give you trouble.
A hardened steel bearing sliding on a not so hard main shaft will lead to trouble.
I purchased a high milage used truck a few years ago,that was always run in first gear.He had the hold clips on the shift rail to stay in first.
when I tore the truck down & removed the shift locks,the shift shaft was almost locking in one position & didn't want to slide any further.
Turns out that the bearing had wore a groove in the main shaft from the bearing always riding in the same place. It was only a couple of hundred thousands,but just enough to mess with the shifting of the trany.
This is just what I've run across since being in this hobby.
FGD