It makes sense, but I'm a bit skeptical because I don't know of any 68040 upgrade for the 68030-socket Macs. Furthermore, I don't know how such a thing would work, since the 601 upgrades do a lot of voodoo with the system ROM and I wouldn't think that it would have the access to do that when going through another set of glue logic.

But, who am I to argue with success? If they said it worked, it probably did. It is an intriguing route to take, at any rate.