An SKS uses a short-stroke gas piston to work. You could only cut the barrel down to the gas block, somewhat similar to the "B*tch" SLR from Australia or (factory-made) Suchka AKS-74Us.
View attachment 505748
View attachment 505749
There would be the possibility of creating an adjustable gas block or a shorter gas piston system, but that's not what the Obrez was for. The Obrez was basically an assassination tool and ersatz handgun during the Russian Civil War and later by partisans during WW2 and the times thereafter, e.g. in combat by the Forest Brothers against the Soviets, Cursed Soldiers in Poland, etc.