I have a 486 DX 33 motherboard in my pc that i'd like to speed up. 
I'd rather not replace the whole motherboard, instead i'd like to know
if i can use a DX/2 66Mhz cpu. The BIOS is late model AMI, circa 1991,
and the system crystal is approx 66.3Mhz. 

My question is, can i just replace the original 33MHz cpu with the new
DX/2 cpu? If its possible, will there be a need for extra cooling
devices such as heatsinks and / or muffin fans??