I think the Type 56 is the Yugo Model, the one with the grenade launcher attachment.
The Chinese government may have referred to one of their SKS variants as a Type 56; it is typical of the Chinese to label things as 'Types'. My Tokarev pistol is a Type 54-1. I think though that the Chinese just called this rifle the Es-kay-es, spoken with a Chinese accent....................
I do not believe the Chinese, at the Norinco plant, made the SKS with a grenade launcher attachment. The Chinese SKSs are typical com-bloc battle rifles. They may have made some nice ones for guard duty and the like but most are battle rifles that are built to shoot and last, and last, and last.
Some will have chrome lined bores, others will not. The spike bayonet is indicative of newer models I believe - older models used a blade bayonet.