a better idea than a fan, would be to fit a specialist head that aids cooling, something like an RC Nova head, like what i have on my eb4 (check the "Hopper" album on my profile).
As to temps on a revo 3.3, from what i have seen, revo's run anywhere from 220 upto 270 (ish), so long as you are in that temperature zone, you should be ok, but try to stay at 260 or below.
My 2.5 engine is happiest when it floats around 270, proving that each engine is different from another, even those of the same brand and spec. Of course, fuel has a lot to do with it aswell, mainly because of the different oil and nitro contents across the many available fuels, each one having a specific percentage of oil.