Then you probably have one of the earlier Sino-Soviet models, or else one which has had parts replaced with parts from another rifle.
Markings.
No. ALL SKS rifles - Soviet, Chinese, Albanian, Yugoslav, Chinese, Romanian, N. Korean, N. Vietnamese and East German - are chambered for the 7.62x39 M1943 cartridge, and can facilitate only that cartridge.
This is purely opinion on my part, but the SKS was created in Russia, and made there for a number of years before the Chinese began manufacture. The Russian SKS tends to have better quality machining than the Chinese. Both are good, but the Russian is the original, and the better built rifle. Examine one of each side-by-side, and see what you think.
SKS
Very similar, minor differences,
The Kalashnikov AK47 and the SKS rifles, 82mm Chinese mortars, 120mm Soviet Rockets.
SN and arsenal markings.
7.62x39mm
By the markings. You can email me at the address on my bio page with photos of the markings, if you should so wish.
All SKS carbines were made in 7.62x39. As for value, anywhere from $100 to over $1500, depending on where it was made, overall condition, rarity, etc. The SKS was manufactured in the former Soviet Union, China, former Yugoslavia, Albania, Romania, former East German, Vietnam, and North Korea. Adding further to the equation, there are both military issue Chinese SKS carbines, and ones manufactured for the civil market. We'd need a lot more information in order to narrow down the value.
They began production of the Type 56 carbine (the Chinese designation for the SKS) in 1956, and production (for the civil market) continues to the present day.
KBI imported Soviet SKS rifles, but they may have come from other Soviet client states, such as Poland, as a means of circumventing the Clinton ban on guns imported from Russia.