The transfer case ends of those studs are threaded 3/8"-16 - so you can just get some 3/8"-16 threaded rod and make new ones (cut to length.)
There's no really sound reason for that application to have coarse threads on the case end and fine threads on the nut end (there are engineering reasons for doing so - but they don't apply here...) so just replace all six and call it good.
I would appreciate one thing tho - if you can, once you've taken one out to measure it, can you take a couple of pictures with the stud laying right next to a clear ruler, and send me the best of them? It's data I'd like to add to my fastener reference.
Anyhow - that application doesn't require anything exotic - so just regular 3/8"-16 threaded rod will serve.