A SN of approximately 210,000 would mean the gun was made in the modern era of somewhat higher pressure loads. However, well beyond that SN, Parker made Trojans with short chambers--although almost certainly a higher % of 16's and 20's than 12's. And once past the mid-20's, it's really 2 3/4" vs the shorter factory chambers that signifies "modern". One source I have, quoting from an old American Rifleman article, indicates that service pressure on the old 2 5/8" 12's was 9500 psi vs 10,500 psi for the 2 3/4" 12's. (I think we can add 1,000 to both of those figures, because psi back in those days was measured with a lead crusher, meaning it was in reality an LUP figure.)
That being said, I think a lot of Parker owners would tell you to shoot pretty much anything in a Trojan. They're very solid guns, overbuilt in comparison to European doubles. I have an early 16ga with short chambers through which I shoot modern factory 1 oz loads all the time. I don't worry in the least about the gun.
