Just have a look at the clock speed specifications of processor and motherboard. If the mobo is stock (25 MHz) it should do no harm to a MC68040 specified to run at at least 25 MHz (as any 040 sourced from a Mac will be), even without a heatsink. Like Flash! I use a 475 with full 040 but w/o heatsink; no problems within five years. If you have a heatsink at hand, consider to throw it in as it should improve the long term reliability of the system, however