I would do it. Iwould do the following first. Make sure you have a good fan, noise is not a concern here. Make sure the heatsink mounts properly. You might have to take the mainboard out of the case to be able to see it edge on. On start up, go into BIOS and watch the temps until they stabilize. With a decent fan and good contact, there should be no issues.
Some s370 heatsinks have a lip on either side and one such gave me problems on a P3 so off came those lips.
You only have to keep the Duron below what? 80 degrees Celsius? For how long? 5 days? I bet it doesn't get near 60 degrees if the heatsink is mounted well and with a good fan. Don't forget the obligatory thermal goo.
I have a Retail Duron 800 and the heatsink was warped from the factory. Even after lapping, I could see a depression in the center. The springclip was anemic in the pressure it applied. I used it on a P3 900 for a couple of years. Radio Shack sold an identical heatsink for socket 370 at the time.
You can pencil trick the bridges on that Duron and run it at 133mhz bus.
