do you think a reasonable GUI(x?) could be installed?

I didn't know that MacOS 6 and 7 do not make good use of the 68030!

Well you might be on to something

The Macintosh LC-II has a 16mhz 68030 as well

Would Minix work /wo a FPU installed?

Also the Macintosh LC-II has a 10meg memory limit, might that be a issue as well?