Yes, the M means it was recalled by the factory and reworked ..and stamped accordingly. So that's a good thing.
Based on the photo - I'd put it in the "Good" category ...and if its mechanically sound, timing is good, etc - bore looks good - then maybe $ 425 - $450 if you clean it up a little / a little polish won't hurt it ....maybe a little cleaning on the grips or at least some paste wax. If it cleans up real well ...$500 isn't out of the question - in my opinion.
Some of your photos - almost indicate some surface rust ...or maybe its crud inside the crane...but it needs to be taken care of unless its just the photo.