Hmm, I had one of these in my old a2000. Which sold a couple of months ago. It never got hot. Warm to touch, but that's it. I am guessing that something is 'a miss'. Check the crystal to see it it's overclocked. (Hard to do successfully with these cards) It should be 33mhz(as in the pic). The xtal ticks both the processor and copro. So both should be getting warm if its overclocked. If its not overclocked then check your power as well, as recommended.
If all seems okay then the chipset heatsink off an old intel MB sounds about the right size and flavor. Twist it off. Check the tape. Stick it on. Job done!. (Go out for a drive on hard rubbish/recycle day: d'you have those in the U.S?) There is not much heatsink room on the right side of processor cards in an A2000, especially with GVP always deciding to put their processors next to the floppy bracket. A slimline chipset heatsink is a good fit.
gertsy