> If you do move the jumper, you will need to find a 40MHz 68030 and 68881. 
> I don't know how rare these are, or if they even exist.  If you'd like to

There are parts up to at least 50MHz, and 40MHz parts are very common on
later '030 Amiga accelerator boards, for example. Assuming anyone still makes
'030 accelerators for the Amiga (they're probably all '040 or '060 now),
they're probbaly at least 40MHz.

However, all the fast '030s I've seen were surface-mount. If you
have the resources, you might be able to get one mounted to a pcb that
would plug into a socket, or they may even be sold that way (for
prototyping purposes, perhaps).

> motherboard with one that runs at 66.  I can't imagine that there would be
> anything else you need to change.

Any number of things, probably :-)