I am not sure to be honest.
See, if don't know, on the under side of the Heat sink there are raised areas that sit on top of any memory chips and other chips that need thermal padding to dissipate their heat.
Now if the memory and other chips are set in different places (Which will be most likely) the heat sink could cause some major damage if screwed on to tight or the heatsink wont touch any of those chips and they would'nt dissipate their heat properly and could eventually overheat.
Not to mention, the GPU could be off set and again, no proper contact.
If you wish, search Google for an aftermarket cooler.
What is the other card your interested in?
If you don't really want to spend extra cash then i suggest going with the second idea of a different card, depending what that card is.