I'll admit I have no real clue, but I believe no reverse engineering whatsoever can legally be involved in an endeavor like that. That is if you want to release it to the public. Beyond that I believe "doing the same things" is perfectly fine, you're just not allowed to look at the actual original kickstart roms while writing the new code.
Yes, yes, I'm sure there are many more legal subtleties involved and I may be wrong altogether. But hey, it increases my post count.