Underwood serial number 28901xxx

Hard to comment on whether the repairs are Arsenal repairs or not.  The stock does not have any Arsenal rebuild stamps, does it?  I suppose that could be a unit or depot level armorer’s repair if not an actual arsenal.  Could just have been a prior owner?

As far as your hand guards, I have a hard time telling shallow groove from deep groove sometimes without looking at the depth of wood on the end above the riveted mounting plate.  Of course, deeper grooves are supposed to have been the earlier hand guards and then transitioned to shallow because of potential to crack with the thinner wood in the deeper groove.

In your case, all of your hand guards are for UEF, so I’d use whichever one fits and matches the stock the best. Doesn’t really matter if it’s a PU or an MU.  Additionally, since it is a high wood stock, oval cut (Type II) - IMHO, doesn’t matter whether a deep or shallow groove. If it were a T1 stock, I’d say that a deep groove would likely be best and if it were a T3 stock, I’d go with a shallow groove.  Like said before, a 2nd block UEF can kind of have some transitional early and later parts based on how Underwood was putting them together and when.

Also mentioned above, since your barrel date is 12/43, your carbine was likely assembled in 1/44-2/44, but that is also a bit of conjecture and is based on how the trends appeared from barrel manufacture until actual carbine assembly.

Carbine “correctness” is difficult for all of them.  With lateral support between all of them, much of which has been documented, it makes it difficult. It is just so much harder to apply any absolute rule of “correctness” to those 2nd block Underwoods based on reasons already mentioned.

I would almost say…if that Lumb Woodworking stock was on there 30 whatever years ago when you got the rifle, then there is a good chance that the rifle may have come from UEF with that Lumb stock on it.  Some were marked “LW” in the sling cut and some were marked “LW-U”.  You can look at Dan’s reference to the Lumb stocks above.  “LW” were supposed to be replacement stocks and then the “LW-B” for IBM and the “LW-U” for Underwood….but sure have seen a lot of just “LW” marked stocks on Underwood rifles for them all to be replacements.