Hi bestoftheworst,
I'm very sorry, I misread the parts list and gave you an incorrect part number and for that I can only sincerely apologise. What I'd like to do is try and send you the correct part free of charge to make up for the incorrect information. I'll send you a private message to get your contact details and we can take it from there.
For reference in case anyone is looking for Optiplex GX620 SFF heatsinks, the normal heatsink for Conroe & Prescott CPUs is JP911 and the "performance" heatsink for Smithfield & Presler CPUs is UP048.
Once again, sorry for the incorrect information but hopefully we can make this up to you.