Hello matey:
I've pointed out the smd resistor in
this picture.
On the 1240 it is in the "left" position, on the 1260 it is in the "right" position.
There IS no firmware to update on the B1240-B1260 conversion, you just need to install the correct libraries into libs:
One other thing you will need to do is fit a suitable oscillator. The 68040 runs at half-clock speed, ie a 80MHz oscillator will run the 68040 at 40MHz.
This is not the case with the 68060 - it runs at full clock speed, so a 80MHz oscillator would attempt to run the 68060 at 80MHz. Whilst this will probably not kill anything, it will probably be extremely unstable. I'd recommend you start with a 50MHz oscillator, and work your way up from there if you want to overclock it. Best you will achieve is probably around 66MHz.
Good luck! :-)
Regards
Rich