Mine has the number 686, so probably about the same age.
What loads have you found works best in it? I'm using 2f powder.
Not sure of the exact serial number of mine (too many guns to consider committing all to memory), but pretty sure without checking it begins with a 5 and has three digits.
What loads work best? More than I can count. This past weekend shot a round of skeet with mine. Used a Lee measuring scoop, 2.2CC to be exact, for a so called square load. Two scoops of 3F Swiss (maybe 70 grains) and two scoops of 7-1/2 shot, maybe 440 grains, with a tight fitting (11 gauge) card between the powder and shot, and one over the shot.
A good way to start is to use the same volume of powder and shot, aka the square load.
As a reference, I’ve tried the Skychief load and it works, but as far as actual patterns, the two card loading method I mentioned above seems to work as well, if not a tad better, though I haven’t done any scientific testing to compare. I just draw a vertical and horizontal line on piece paper with a circle around the intersection point of the two lines (your choice of circle size) and count the hits in each of the four quadrants.
Best way to figure out what load(s) work best in your particular gun is to go out and shoot it. Unless you are looking for just one load, keep notes and pay attention to them. Not rocket science.