If I'm not mistaken it's tricky to do this upgrade, you need to reflash the cards firmwarewith the correct firmware.
The 68040 and 68060 cards have different firmware.
I sent a 68040 CS MKII to PG, the guy who did all those excellent BPPC and Apollo '060 upgrades...he failed upgrading my card...it never booted with a 68060 CPU on it..after doing some googling we found out it needed a special firmware which can't be found anymore 
Sounds risky in that case. :/ Maybe later manufactured '040 cards came with a firmware compatible with both processors. I suppose you could make an educated case as to whether or not it would work, if you compared your card's serial number with someone who has successfully made the upgrade.
