it all really depends on how much you really wonna get this thing going.
1. You could buy a proper heatsink (although nothing fancy there are a couple of them that you could purchase). easiest option
2. Try local used computer stores (this requires work...
calls and whatever)
3. if you realy don't care and this is a "bonus" system. Try make the coolers fit, the main thing is for the cooler to have good contact on top of the CPU (evenly), try fit it without the thermal paste first just to see how it goes, if it works you could always do it properly after. How close or weather they actually interchange i don't know. from wiki page on 478 socket, it would seem they are the same; 478, 478b, 479.