I am planning to buy a Marutaka 1/5 scale L-19 (88" wingspan, 10-12 lb) and it calls for a .60-.90 two-stroke or a .1.20 engine if using a 4-stroke. I have an opportunity to buy a Saito 1.00 opposed twin, used twice, for $300. Would this be enough engine for a plane this size?. I'm looking for adequate power and maybe a small reserve, something that will give scale flight performance.

Twins have somewhat less power than the same size single.

I see this engine as being very marginal as to it's ability to fly your plane in a satisfactory manor.

Jim