I would be more concerned with whether these winches are going to look too big bolted to the combings on your boat. I thought that my Barlow winches were #13s but I suppose they could be #15s. I'll check tomorrow and get you some outside dimensions that you can go by.
I'm sure they'll look fine. As for where to mount them; what I would do is stand in the cockpit at the tiller and lay the winch on the combing. You want it within a comfortable reaching distance from the helm. There aren't too many choices as to where you can place them, but those horn cleats will have to be removed. I would also place a large open clam cleat directly behind each winch. You'll love them, believe me. My friend Wayne had jam cleats behind the winches on his Seaward 22 and he replaced them with clam cleats and he loves them. Most of the time you're going to use these winches like capstans, operating them without a winch handle. You'll get into a steady routine while sailing single handed. You'll tack and release the sheet from the clam cleat as she goes over on the new tack, and pull the sheet straight up off the winch. As she settles in on the new tack, you'll put a single turn of the sheet around the winch, pull the slack out and put two more turns around the winch, set the sail, and put the sheet in the clam cleat. If you're beating up wind, this becomes automatic. You don't even have to touch your main sheet. Just let the Mainsail come around by itself. This is why it's so important to have the winches within a comfortable reaching distance. I have a Davis Windex on a 12" extension bracket at the top of my mast and I'm constantly checking it, especially when I'm sailing down wind. Good luck!
Yes, 24 of anybrand is overkill for a smaller boat. However, since you are commited get piece of HDPE about 1" thick and mount winchs to Hdpe and mount hdpe on gunnells. At same time make sure piece hdpe is long enough to mount cleats on it too.
