Paul, I stopped by and had a look at them today. Harbour Yachts was closed so I couldn't get below on any of them - you'll have to go by the listings for that.
Of the two 27's I'd say Mr. Duck is the better one. Trincomali is noticeably scruffier - I'm not at all sure the gelcoat could be buffed back to a shine - that pale blue gelcoat C&C used back then never seemed very durable. Mr. Duck I think could be - it still shows some shine. As for deck equipment they are pretty similar. Mr. Duck has a better looking dodger with window covers. Their bottoms are about the same - need a good sanding & new paint but otherwise look fine. Mr. Duck has a better looking prop. Trincomali has a new looking, lifting outboard bracket. They both have jib furling.
The Grampian is by far the scruffiest of them. I think it would have to be painted - it's showing a lot of print through due to the gelcoat being thin I think. Of the 4 boats I'd place it last but it's also the biggest and has a big diesel so.... It does have a small rig - 126' less than the C&C 30 which is a big deal around here, as you know.
The C&C 30 looks in pretty good shape. Apparently it has been docked portside to for much of its life
It has a winch farm on deck A La early IOR. No furling, just hanks and it has an Atomic Bomb, if you're one who worries about gas engines. No dodger on it either. It's the only one in the water so I couldn't check its bottom. The ports will all need redoing - the lens gaskets are all pulling out of the frames. Actually, ALL of them will need their ports redone if you care about seeing out.
The 30 has a nice alloy front hatch where the 27's have fiberglass ones.
Considering they're all basically the same price - $10 - $12K asking, I think the C&C 30 has it, hands down. Unless there is something ugly inside like a dead or dying engine etc. it's the one I'd go for (even though it's yellow) - it's a lot more boat than the 27's and a lot nicer and better looking than the Grampian. Dodgers & furling are expensive though if you have a strong need for them - easily $5K unless you can find something used.
They're definitely worth a trip over to check out to see which one suits you - they all look like pretty solid boats from the outside and the C&C's all appear to have been loved most of their lives.