It's really easy to explain why the Zenoah engines are much heavier than the others which you are looking at.

The Zenoahs are basically industrial engines, from applications where weight in engine design was not a factor. However, being robust, with a maintenance free, long life is what counts there. So there's no problem using a magneto for ignition, building a large, sturdy, heavier crankcase, crankshaft or two ringed piston. Years ago, near the start of the gasoline/giant scale movement, they were adapted to model aircraft use, following the introduction of the Quadra back in the late 1970s which got the ball rolling.

The others do not use a magneto, have a much lighter, smaller crankcases, tend to use fewer bearings on the crankshafts and use one ring pistons instead of two ring pistons. Fewer parts. Less weight. However, once you add in all the other necessary stuff, such as ignition box, its requisite battery and optical kill switch, there is not a massive weight difference between the Zenoah engines and the others. Mind you. they are also less highly stressed since they do not put out as much power as the current designs. But then, they are also much likely to last much longer with less maintenance over their lives.

Have you ever actually checked the actual weights of any of these engines and accessories against the manufacturers' claimed specs? I have. And in most cases, the actual numbers were higher than those claimed. And in several cases, they were significantly higher. Paper claims mean very little. It's the actual numbers that count.

As for the DA50, that may be a bit too much engine for the plane. Basically, the fuselage is constructed of 1/8" lite ply. There is not any real aircraft grade ply in the plane. That includes the firewall.

I've got a Super Tigre 2500 in mine. And I can assure you, even with that, I've changed the nose and firewall construction to ensure that there are no surprises with construction or wood parts failure.