Well you need a laptop version of the CPU which is harder to find then a normal one. On top of that, K6-2 CPUs in general have become something of a rarity. & finally when you take into account the fact that laptop CPUs aren't meant to be swapped with newer ones, you'll notice you have a lot going against you.
If you insist on looking for one anyways, I guess you could pretty much take any K6-2 all the way to 500mhz & adjust it to a 66mhz FSB. The Socket CPUs before the Slot 1/A era did not have locked multipliers so you could play around with it & the FSB, provided the laptop's BIOS / Mainboard lets you do so.
Just bring the new chip down to the same speed as the old one & gradually raise the speed while keeping an eye on the temps. If your laptop was designed with a certain CPU speed in mind, it might not react very well with a faster, hotter chip.
I still think it might be a better idea to start saving for a newer laptop though.
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