hmm, you'll probably have to contact the manufacturer of the heatsink you want. just eyeballing it, the screw holes don't look like they are spaced the same way.
Thanks for your answers...well I'm not replacing it actually, I need one I had a 478-compatible heatsink and I thought I could use it on the 423 Mobo. I know it's ancient but a 1.5Ghz Willamette PIV can still run Win XP easily...