I superglued homemade heatsinks to the 3 GPUs on a voodoo2 & had no problems.. they're still on tighter than hell..
I also superglued some homemade heatsinks to the memory chips on a voodoo3 3500TV & they're still on tight.. heat doesn't seem to be much of a problem for it.
The way I did it was I used some ASII in the center and some superglue on the edges. I think you can also mix the ASII & glue and just use that all over. I've read about people doin that way, but never tried it.
If you're just gluin a fan onto the heatsink, they're shouldn't be any prob at all..