Hi!
Whatīs important when building a scale model and certainly more so when building a twin engined airplane is building it light! Light planes always fly better than heavier planes and last longer!
People seem to forget this and use too heavy engines on their planes thinking "I could always throttle down" and thatīs a wrong way of doing it!
So...using large heavy petrol engines is no good if you want to keep the plane for any longer time.
Instead use the smallest, lightest engines you can have, but of course with adequate power, and that is why you should use a pair of .70 four strokes and propping them for around 9000-10000rpm (13x6 two blade or 12x6 three blade).