what a great situation to be in.....to have a choice of good quality 2nd hand sails.
Jim is absolutely right....if you have any chance of actually trying the sails out, then I would suggest you do so. I have had a bundle of 2nd hand IC sails over the years and found that some looked 'great' but were just horrible to sail with, whereas others have been so nice to sail with that I continued with them even to the point of them being full of holes.
Hopefully, you should be able to talk to the owners and find out whether they worked for them. I have bought sails which were in great condition....but they were development sails and just didn't work at all and I doubt they ever did.
You also need to check what the sizes of these mains are......and correspond them to your jibs....to try and make sure you stay within the allowed size. You feel cheated if you are too far below it....and of course you are cheating if you are above it
As for fat-head vs normal.....I think you really have to try them and see. nonetheless, I find it interesting that although fat-heads seem to have been often tried out....they have never seemed to become standard across the fleet. I have only tried one once, and although it seemed quite powerful and did 'feather' more, I found the extra canvas up high, made it noticeably harder to tack with, which lead to a bit more swimming. But, to be honest, I am a truly crap IC sailor and enjoy anything that makes sailing 'easier' and avoid anything that increases my swimming time.
It might well be fine for you....only a test sail would really prove it one way or other.