I think people use 40mm fans with M3 screws that just bite inbetween the fins on the heatsink slightly. Seems to be the usual way I see in pics, otherwise I have seen one or two secured with long zip-ties wrapped around the motor,heatsink & fan.
well I might not be putting on the brushless set up on my e-revo I have the feigao 9xl motor but no esc yet but my cousins neighbor wants to trade me for his 1/6 monster buggy with a 23cc zenoah weed whacker motor and tuned pipe very tempting I always wanted one but they are too much from the get go... maybe down the road I will do another one I just love how easy it was to work on and build
well he did not want to go threw with the deal so now I am looking for a good brushless motor,esc, and battery set ups also for batteries no lipo even though they are the best option