I don't think it's worth it to convert a frame with a one-piece BB shell, especially if you're going to go all out painting it. If you want to convert a beater and the stock cranks are already there and working, then maybe it's worth it, but you could find a better frame for $10 at some thrift store.

That said, it would be kickass if you could get some cartridge bearing of the correct size, press them into the shell at each side, and then use modern 2-piece crankset like Hollowtech. This is basically what the newest version of the Trek Madone does. But.. the shell width is probably wrong, you probably can't find the right size bearings, etc.