Mate, it depends on just how the readings were taken. A good engineer would take them when the engine was warm and if values like that were found, they would give the valves a hit with a soft hammer to make sure the valves were seating properly, they are the most likely cause of a low compression. If however, those values were the best an engineer could get you might want to look at something else, but then again, throwing 2 o/h'd cylinders on it would be a cheap option as well.
I would have the readings taken by someone else when the cobwebs are blown out of it, an engine with 840hrs since factory new shouldn't give you too much trouble. If it does, it is probably indicative of the treatment the machine has been given.
Sorry to waffle on. All the best.