RE: twin seamaster engine size?
Back when RC Report was a print magazine and I wrote a monthly column, my flying buddy, Carl "Flaps" Laffert, I did an experiment on out thrust. My test plane was a Goldberg Tiger 2 (.46 size). We added 2 nacelles and covered over the engine compartment. Power was 2 OS .46 AX's. The nacelles were built with 8 degrees of out thrust. Total weight-8.5 lbs.
I realize that 8 degrees looks huge and most people would think that you'd lost a large amount of forward thrust. I did the math and the cosine of 8 deg. is .99027, meaning you have a tad over 99% of your forward thrust. I confirmed this in flight to the best of my ability.
For testing, once the plane was trimmed and I had gotten used to it, I filled the left tank 50% full and the other, all the way. Then I cranked and took off and flew my usual aerobatic flight. The idea was to see how out thrust helps without knowing when the engine will quit. When the left engine quit, I didn't notice anything except a loss of forward speed. No yaw, no nothing. Next, the right tank was filled half way and the left all the way and the test repeated. Same results. Out thrust worked great.
At a later date, I built a Twin Stick ARF, also with 2 OS .46 AXs and 8 deg. out thrust. It turned out a pound lighter at 7.5 lbs. It would easily do any acro I wanted on a single engine.
I will admit, the looks of 8 deg. out thrust will scare you, but after several planes using this amount, I am convinced.