Hi, I would be glad to help you any way that I can by answering your question to the best of my ability.

The difference between the SKS and the SKSS is only in the gas system. It is probably a regular Paratrooper. But the SKSS can also found in the sporter and SKS-M versions. These actually have been fitted with barrels that have a different gas port position, and hence the shorter gas tube/piston are needed. The "space" that is between the rear of the bayo lug and the gas block on the SKSS is not present on a regular cut down paratrooper.
It was not so much that the length of the tube was thought to be needed for alteration (stroke distance = same as standard SKS), as it was the gas pressure that developed after the bullet passed by the gas port. The further rearward that the port is drilled, the more gas pressure can build up for reliable cycling of the piston/operating rod/bolt combination.
But when it was evident that a normal cut-down barrel did not impede cycling, the later paratroopers simply used the existing gas port and standard length tube.
Trigger assembly should be the same as the Norinco SKS model.