All good points you're making. I admit my experience with transfer cases is much more limited than my experience in other areas.
That said, the jumping out of gear deal is typical of worn pads on the shift forks.
Since yours has so much 4wd usage as a plow truck, it would stand to reason that your chain would be suspect. That's much harder use than the average truck gets.
I think the reason you only get bearings and seals in the rebuild kit is that basically that's all that wears on these units (excepting the chain). The oil pump is typically reused upon rebuild. The kit comes with the new oil pump seal and o ring for the pickup tube. Once you remove the bearings, seals, chain, and wear pads on the shift forks, there's not much else to fail.
As far as the bearing deal and 241bk vs 241bk-a, the guys at my trans shop told me the early units like mine with the wide bearing were not common at all and the narrow bearing was used in the majority of 241s.
The deal about your truck being your only wheels is deal deal breaker though. I agree that it would be a bit sketchy to dig into your transfer case knowing that you're afoot until you get it back together. You seem like a very hands on guy with your history of rebuilding stuff. I know I very much enjoyed the transfer case rebuild project. Maybe you could find a good used core and rebuild it at your leisure then just swap it in place. In the end, you'd be happy knowing you had a fresh case under there that you rebuilt personally.