Generally speaking if you sell something like an M1 Carbine for a scuba reg, you will regret it later.
Inland M1's are commonly encountered. From a collector standpoint, much of the value depends on how correct it is. A new mil spec replacement stock may not totally kill the value of a late issue Inland carbine - if the stock is correct for a late WWII or Korean war Carbine. However, for an early Inland with otherwise all correct early carbine features, it would impact the value. You do lose the cartouches with a new replacement stock, but they often disapeared in service anyway, particularly on weapons that spent lots of time in the company area and were excessively polished and refinsihed.
Most M1 Carbines saw at least one arsenal rebuild and in the process lost early features like early style sights, thin barrel bands, barrel bands with no bayonet lug, single rivet hand guards, push button safeties, flat top bolts, etc. In addition, many were exported to friendly nations as military assistance and then re-imported for sale to civilians. Since about 1990 or so, they have been rerquired to be stamped with the importer's name which lowers value. Some importers stamp the barrel where it is visible, others stamp it under the handguard which reduces the impact on the value of the carbine.
Consequently an early all correct WWII issue carbine with no import marks can bring a lot of money - maybe $1500.
At the other extreme of desireable but for different reasons, a reparkerized carbine with later M2 parts and a new pot belly M2 stock in minty rebuilt condition can still bring $500-$700.
The low end of the scale would be a well used M1 Carbine re-imported from Korea with not much original finish, a beat up ratty stock with oil soaked stock, non matching handguard and a rough bore. It would still bring $150-$200.
