RE: Aviastar 46?
We have used 4-strokes on twins, too. Mike109 has some excellent points. We tried a couple of Mag .30 4-strokes, but could never get them to run together reliably. The Magnum .52 4-s run great in twins. We've had our pair on a couple of scale twins and never had an engine failure in flight except for my flying too long and running them out of fuel.
I also have several Saitos and they are really reliable. I tend to use 4-strokes on seaplanes so I don't have to paddle out when they quit on taxi back. I have a .56 and it is excellent. My buddy Flaps likes scale so he tends to snag all the 4-strokes. He's 89 and I do all the flying. I like faster sport, twins, seaplanes and Sticks, love Sticks. Anyway, I tend to end up with the 2-strokes, except for seaplanes.
I bought this nice little Thunder Tiger .75 4-stroke. Good running engine. I broke it in on my bench for about a half gallon of fuel, then flew it in a plane to further run it in. Next thing I know, Flaps wants it for a scale project. It's a short engine and won't stick out past his cowl. That's where it is now, in a 72" radial engine version of a Fairchild 24.