Do yourself a favor and avoid the heatsinks in favor of just servo taping or shoe gooing the fan to a spot on the chassis to blow on the motor and/or esc. Plenty of reference photos all over this board, especially in the wiring thread. You'll be MUCH happier with the overall results and not have to take the weight penalty. Most of the heatsinks out there will do little or nothing for you at all other than simply hold the fan and get in the way of proper airflow. I've got a box of the little things from all over, of all types, and nothing ever worked anywhere near as good as a naked fan blowing on a naked motor.
Since the 25mm Boss/Geisha/Fantom fan supply dried up, that's been the de facto replacement 30mm fan. The Muchmore fan(even the super duper one) is muchmore fragile and moves muchless air! Been there, done that, would be happy to give you the POS muchmore if you'll pay shipping.
THIS is the current replacement for the Boss/Geisha/Fantom fan...and it's pretty amazing. Same form factor(25mm), but moves more air on less voltage. The only down side is that it has to be powered through the RX on the BEC supplied voltage. That may or may not prove to be an issue. Probably more of an issue with guys running the Savox/Spektrum gear that requires an external cap to prevent brown outs (not all do), as the cap will use the 4th slot in the RX and compete with the fan(steering servo, ESC, transponder, and open).