I am not sure if the original poster got a 68CL040 chip or not, but if not, I think I have one that may work, if you want.

I had both a 520c and 540c that worked, but I canabalized the 520c case to make the 540c cosmetically better.  I have the 520c motherboard, processor, and Ram (the RAM and processor are still attached to the motherboard).  It is listed, however as 50/25 mhz, so I assume it is slower than the 540c's stock 33mhz processor.  Would such a thing even work if plugged into a 540c board?