Third gear not working - found this in tranny

[WilsBoar]

It may be the rear layshaft bearing judging from some online pictures. If so, there are some random parts still floating around that may be the culprits for jamming up my 3rd gear...at least.

[I Leak Oil]

That's a possibility. That bearing is small compared to most of the other bearings in it. I was just looking at an old set of bearings I have. The part you pictured could also be bits of the roller bearing between the primary input and the main shaft. That's also where the 3rd/4th syncro is so that could be causing your shifting issue.
Judging by the size of the rollers in the picture, it's most likely the layshaft bearing though.

[WilsBoar]

Thanks. I guess it is a certain rebuild. What should I expect to pay for a rebuild?

[Max(SD)]

I am doing a rebuild on a SII gearbox, I have removed everything. I am replacing two gears, all the bearings, one layshaft, all the rubber seals and all the gaskets. I have had all the various gearbox and transfer casings washed and cleaned, I am also replacing the u-joints on the front and rear prop shafts. Since everything is apart I have sent some parts for powder coating, new clutch, some new nuts and bolts, and refinishing the old nuts and bolts. This is probably going over board, but I figure everything should come in slightly under $800. I took gearbox apart in pieces, but I will probably put everything back in one piece and have to rent some type of lift to put back in the truck. But I don't seem to be moving very fast, as life is constantly moving around me, and I might get a couple of hours here and there to concentrate on the truck.

Take lots of notes, take lots of pictures. Taking things apart is easier than putting them back together, especially taking dirty oily things apart are look different when things are clean and new. When I took the transmission brake assembly hardware apart, I did not take too many pics, and I regret that, will probably come back to this site for help, as I got all the pieces powder coated, will certainly need assistance putting it back together.

Best of luck.

[I Leak Oil]

Thanks. I guess it is a certain rebuild. What should I expect to pay for a rebuild?

Depends on what needs replacing. At a minimum I'd replace all the bearings, bushings, seals and synchro. Gears for first and reverse are common to have to replace.
Your labor is free, if you have to pay someone it's probably best to buy an already rebuilt unit.