No offense intended to any of the posters here, but you're not getting good info on your rifle. It's a 99EG if the forearm is correct and numbered to the rifle. You can check by removing the forearm screw and forearm, and looking on the end of the forearm nearest the receiver. It should be stamped with the same serial number as the rifle. The buttstock will have a number under the metal buttplate. If they match, congratulations, you have an uncommon and somewhat hard to find 99EG in 308. 1956 is correct for the year.
There were rotors made of materials other than brass pre-mil, or pre one million serial number. For example, around 1954 there was a run of case colored rotors.
After serial #900,000, which is about 1955 IIRC, the receiver was modified to accommodate the 243/308/358 cartridges. After 1960, or after serial # 1 million, "post-mil" to 99 guys, cost cutting measures began to erode the quality of parts and workmanship in the 99's. However, the addition of the tang safety in 1960, on all models except the economy "E", redesigned and moved from the earlier position by the lever, made the 99 a little more user friendly for leftys, and was more familiar to shotgunners accustomed to tang safeties. I find the tang safety to be a mixed bag. It's a little harder to get at with a scope mounted, but a little more intuitive in it's location than the lever safety.
I'm not trying to come across as an expert, I am just learning myself, and am passing along what I am learning so that you can know a little more about your firearm. You should not sell your 308 EG cheap, it's a desirable model. Should you decide to part company, I recommend a penny start Gunbroker auction with no reserve and no Buy Now price. You will attract LOTS of attention very quickly, and your rifle will sell for more than you think. At any rate, your rifle should be an outstanding shooter.