Tabushi,

I use a GTB in my 1/12th...here's how:

Remove the 4 screws in each corner holding the heatsink on.
Disconnect the fan (connection next to sensor harness slot).
Remove the heatsink and fan.
There is a small "pad" between the heatsink and the ESC. Don't lose it!

Now, using the heatsink as a templace, cut a thinn piece of alloy (I used 2mm) and drill 4 holes in the corners, so that they match the holes in the original heatsink.

Use the crews that came off the heatsink to hold yours in place (remember to use the "pad" between the ESC and your new heatsink.

Now you have a "one of a kind" heatsink - must be faster!