I've been looking for plans for years, and no one really seems to have them available. The only thing that came close was the Swedish Stradavarius, and there, the designer wanted to sell molds, not plans. S&S said that the price for designing one (they had no stock plan) would be the equivalent of the price for a 6mR or an 8mR, as they'd have to do the same amount of work (including tank testing!) no matter the size.
In the 2.4mR world, the thought is to go with a Norlin Mk III, as they seem to always win. The class came very close to becoming a one design because of this just a few years ago.
On the other hand... see the Dragonship/Meerkat thread in building and design. After all, it's only a 12 foot boat, if it doesn't work out quite right, and you're not planning on winning regattas, how much are you out? The only thing stopping me from doing the same is time.
Info on the rule, how the boat is measured, what is required to become a "real" 2.4mR is found on the 2.4mR web site.
To answer your second question, while scaling down directly wouldn't work, there's no reason that as you're designing you're own, you can't make it look more "classic". Classic topsides with modern below the waterline is the latest thing in the 8mR class. For that matter, I can no longer find the web site, but if anyone has copies of Sailing World from 2004, somewhere in there, a company announced the design and manufacture of a J Boat scaled down to 15 feet LOA, sailed like a 2.4mR. They wanted an awful lot of money for it (which is probably why I can't find their website anymore), but it did look like a lot of fun!
I won't be wronged, I won't be insulted, and I won't be laid a hand on. I don't do these things to other people, and I require the same from them."
- J.B Books