What is the wing spread and the weight? My guess is that if it is a 60 size, that you will want a 91 four stroke in it. The 61 4s is just about a 45 2s size in power. You don't need the speed, but you do need the power. A Mag or OS 91 would be a good engine, as well as a Saito.

For what it's worth, I built a Great Planes Super Aeromaster bipe. It weighs around 9 lbs and has a wing span of around 50 inches. It called for a 91 to 1.20 four stroke. I had both, but I couldn't figure a way to get the 1.20 on the firewall. I ended up with the 91. Haven't flown it yet, but I'm afraid that it may be a bit underpowered.

Don