It'd definitely be a challenge. The 12" Powerbook is, of the aluminum machines, the largest pain to work on. Everything is contained within the bottom case, which means you would have to strip the entire machine. Beyond that, you'd have to craft or have manufactured, a new bottom case that was to spec. By that I mean that it would have to fit everything, and have all of the screw mounts in place so that everything could be held into place.

If you've got some serious metal-working skills, possibly. If you have a bottom case you can give to a manufacturer in order to have a duplicate made from a secondary metal, sure. By hand, I dunno.

In regard to the whole ibook bottom case on a powerbook, the short answer is no. they're 100% different.
Electricity tastes good. No, seriously.