David, I guess my original question was poorly phrased. I mean that the big 2 strokes with pipes, but the 4 strokes with regular mufflers.
I put it that way because the modern 2x2 pattern planes, including the LDIII, seem to be geared towards the big 2 strokes with pipes, and was wondering if maybe a 1.2-1.8 4 stroke would be enough power, or physically too big.

The plans I got from RCM with using non-piped 2 strokes or 4 strokes in mind. I really like the classic pattern aircraft look.