Does it look something like this?
Google "Cutts Compensator". They don't all look exactly alike, and the tighter chokes are longer. Could also be a "Poly-Choke". I have no idea if it's factory, but I'm sure Google can tell you that as well.
I have also wrestled with the messing with history dilemma. I don't think there is a right or wrong answer. If the gun is not historically significant, and you're not going to use it as-is, does anybody but you care? For example...I have my Grandfather's Remington 722 in 222 Rem. It was the rifle my Grandfather/Dad/Uncles shot 2200 rounds through in one summer, as calculated by the empty powder can generated during that time. My Dad figures it has 15,000 rounds through it. A borescope reveals the throat is ok and doesn't look to have 15,000 rounds, but the 4" closest to the muzzle are trashed. The current accuracy is not up to par with what it used to do, so it just sits in the cabinet. If I don't shoot it, my daughters won't give a rat's ass about another rifle in the cabinet, they never knew my Grandfather. I'm debating spending way too much money to have the barrel rebored and bolt converted to a short action hunting round so my daughters can use it, and will therefore treasure it. The problem is that the money to modify the old 722 would buy each of them a Tika/Howa/Savage in 6.5 Creedmore. Since I'm a sentimental fool, it is still sitting in the cabinet, same as it ever was for the past 18 years I've had it.