Saw that but even with a bottom job (that price quoted could have been for blister removal and barrier coat because that is really high!). Bottom paint (good ablative paint preferred for fresh water averages $150 gallon @ 2 gallons for that size boat is $300. Where it got to 8-10K had to lead to repairs! I guess the current owner would have the details. Given all that, it is a bargain at that price. The C&C is an excellent blue water boat and the hulls back in the early 70's were built thick because glass was fairly new as boat building material. Today its a whole new ballgame!! During that period the Ericsons, Pearsons, O'Days. Morgans, Cal, C&C's to name a few came on the market. The early Hunters and Catalina's were the lower end; sort of the Chevy's of the fleet. Sorry to say, McGregor came in at the bottom on quality of materials.
Parts are still around for the Atomic Four, which was the workhorse of the day before diesels were installed. You just have to make sure the tank and ventilation system are up to standard and your fire extinguishers are working! Interiors can be revamped, especially if you avoid the costlier Marine Parts catalogs and shop at RV stores for pumps, hoses, lighting, etc and all things DC powered. Big savings their.
If I were in your shoes Daddle, I would certainly consider this C&C, but I personally would still dive the boat for a look see and get the hull/bottom repair details. In a fresh water environment the standing rigging and stanchions will not see corrosion but you do not want the mast falling on you either! Take a close look at the swag fittings and BTW the big thing now for re-bedding stanchions is butyl rubber. Looks like you have roller furling which is a nice touch if a storm comes up. You have been around boats as long as me so you know what to do. Like you said, the engine is key, but their is a ton of info on the Atomic 4 on the internet. Everything else is simply
.......................messing about in boats
fair winds