RE: Sig four star 60 engine choice.
I used a Super Tigre .90 on mine. The logic being that this engine is the same size and weight as many engines in the .60 - .70 range, and so there was no wieght penalty for the extra power.
If you want a gas engine, as apposed to glow then you could consider BME Super Tigre .90 gas conversion - [link=http://www.bmeengine.com/engines.htm]http://www.bmeengine.com/engines.htm[/link].
I don't know how it performs but there are some post on here and other forums about it.
Apparently it can run at full throttle for 3 mins and only burns an ounce of gas! So you'd pay for it pretty quick over burning glow.
Good luck.