Two gas (weed whacker) engines may be your only way to go. At least with the pusher engine. Rear engines can get hot when ran static for any length of time, and if your plane is scale and rear cowled I can't see that helping matters any. With the weed whacker engine it may work if you keep the cooling fan/housing and place diverters/ducts in the cowling to help the fresh air moving along, keeping in mind air flow when it's in flight.

Pusher props small to large 2,3 or 4 blades:

http://www.zingerpropeller.com/index.htm