Value? You know the answer to that. What ever some one is willing to pay. Go ahead & check the gun auctions or the Blue Books to get a range. If you want a number I'll give you mine.
What you described is not worth $250 to me. I've seen 97% & up guns with boxes go for $350. Although the last Trooper MK III I bought was $400. But it was pretty nice (almost perfect) for a 1971.
I don't have any reference material with me right now for S/N look up, but I know that it is 1981 or before. I suspect within 1 or 2 years. Is the top of the barrel flat or does it gradually ramp up to the end of the barrel?