Take a look at
http://www.telusplanet.net/public/bboogaar/
flathead.htm for some info on Ford flatheads. Why would a person want one? Couple of reasons: When they came out in '32, they were the hottest affordable engine around. Held that position for a long time, so many guys grew up with them being 'the' engine. When Chevrolet came out with the 265 CID small block V-8 in '55 they took over that distinction. For some of us latecomers, the flathead is different enough and funky enough to be fun. Myself, I'm a bit of both - grew up with the last of the U.S. flatheads ('53) in my pickup, but it was already 20 years old by that time; all the other guys were into muscle cars by then.
Flatheads (or L-heads, as they are more technically known as) are not nearly as powerful and efficient as an overhead valve engine because of the path the fuel/air mixture has to take to get from the valves to the cylinder, so when a good, cheap overhead valve engine (the SBC) hit the market most flatheads became boat anchors. A lot of wild things have been done to flatheads to boost their performance, including replacing the heads with overhead valve heads! More common mods were multiple carbs, boring and stroking, and blowers. Some vintage-style speed equipment is still being produced today.
There is a real quiet newsgroup on Ford flatheads: alt.autos.ford.flathead
