I have a good front 3rd member with a tight pinion bearing and I have a broken rear ring/pinion due to a bad pinion bearing that gave out on the trail. I am looking at swapping my good rear carrier and spare ring gear into a front 3rd housing with good pinion gear/bearing.  Just want to double check its do-able first.

The other hang-up is there is some light dirt/debris in this front pinion/bearing (been sitting on my work bench) that looks like a pita to clean.  I dont want to guess that its dirt free and MOST definitely do not want to do this again for a while.  I thought of taking the driveshaft flange off so I can clean it thoroughly (flush out both sides of the bearing) but probably next to impossible on breaking the nut loose with nothing to hold against (carriers already removed).

Yes, the carriers and gears will interchange between front and rear thirds.
From what it sounds like, you are wanting to reuse the existing pinion that is in the front third and swap in another ring gear.  That is a big no-no.  Gears are made as matched sets and should not be mixed and matched.  I'm not saying that it wouldn't last the life of the samurai, if you mixed and matched gears from 2 different thirds, I'm just saying that it is not recommended.
Also, if you remove the pinion flange, you need to make sure the pinion nut is put back to exactly where it was before it was removed.  That way your pinion bearing preload stays exactly the same as it was before you took it apart.

Thanks for the reply.

I think I will just pickup another rear diff. They are easy enough to obtain. Its sure no walk in the park to do it all over again.

Thanks for the reply.

I think I will just pickup another rear diff. They are easy enough to obtain. Its sure no walk in the park to do it all over again.

That is a good choice.