From my experience with IBM laptops, it is worth a try, but:
- first, make yourself comfortable with removing your present CPU: if you can't remove it easily, you won't be able to replace it anyway
- check that you won't need any special thermal compound to stick the cooler back on the cpu
- ensure that it is a 440BX chipset you have, otherwise getting a 500MHz cpu will be useless (if you have a ZX chip on your granny laptop, you're out)
- I would guess that the price of the replacement mmu would be quite small. Get it and try: if you can get the system to boot, you're a winner. If not, you've just set yourself a few bucks back... on a free laptop
While IBM series usually follow very close hardware specifications, changing the cpu is not that easy.