Hi!
A glow engine is much lighter! Gives Less vibration! Which means you don't have to build as strong and heavy as with using a gas engine.
The only thing better with a gas engine is that it requiers less fuel which means smaller tank and less weight.
But I would still recommend using two two-stroke glow engines because they weight less and low weight is very important in any plane and more so in a twin.
The RCW .90 is not suitable for your plane as it needs lots of cooling air to function well!
...So forget about any three blade props and go with two good .61 two-strokes (i.e Kyosho GX.61 or OS.61) 13x5 or 13x6 APC and RAM props!
12 oz tank, preferable set up with two clunks (Uni-flow set up) or better still (But not needed) a Tettra "Bubbleless" tank!