Primers back then were either corrosive or mercuric.  (Some, If memory serves, we’re both.)

Unless the compounds have decomposed enough to corrode the primer cups and the surrounding pockets, the shells should be OK.

There was a phenomenon called “season cracking” which typically occurred in hastily produced wartime ammunition where the brass hardened over time and cracked where the necks were strained by holding the bullets over years of storage.  You might do a mild anneal of the shell mouths before using them, just in case.  Otherwise I would say the cases would be fine to use.

28-30 brass is hard to come by, but originals in a 2-piece box has some collector value.  I'm a cartridge collector and a 28-30 shooter. That would be a hard call, but I'd think the collector value of scarce cartridges in an original box will increase and their value as cases decrease.

That said, I've been shooting a 28-30 since 1968, and for many years used only original UMC cases.  Many of mine are still OK, but many, many extractions has worn some of the rims.

28-30s are straight taper cases, so much less likely to develop stress cracks than BN cases.  Bullets are lead and are much less likely to bond or crack case necks than jacketed bullets. 

I would pull the bullets with an inertia puller.  Save them, because original samples are pretty rare & you can learn something from them.   

Inert the primers with warm water, warm because it is more chemically reactive than tap water. Using penetrating oil (Kroil?) would do a better job of killing the primers, but it might be difficult to remove 100 % of it from the primer pockets & it might keep on working.

After that, enjoy your 28-30.   

Since I understand that no one has loaded 28-30 since WW 1 these have all the negative attributes. I guess I ought to sell them since I already have 90+ Australian manufacturered cases. I lost a few during forming, started out with 100.
I also have an Stevens English model in  28-30 with a perfect bore that I've never shot. Until a cataract surgery I needed a scope and couldn't bring myself to drill and tap for mounts