The 8x ones seem to be in the highest demand due to their use on military rifles. I have a few original external adjustment scopes that I use on my single shot rifles. I prefer a lot more magnification, but like I say, the 8x get a good price. If I owned it I wouldn't think of selling it for less than $800, probably more. The lack of a recoil spring will reduce the value a bit, but yours seems in very good condition.
Chris.