Of course I can't remember the details (like the URL or the person who did the work) but there's a fellow with a website up where he cloned the hardware. He took each of the custom chips on the logic board and rebuilt them out of non-Apple components and wrote out the logical equations that describe the chips. And he breadboarded together a Plus board in the process. I do not think that he rewrote the ROM, but I don't remember. I'll try to check to see if I have the site bookmarked when I'm home, but my memory is so leaky...

I want to say it was an Aussie who did it, but I may be misremembering.