Hello!
If I was to construct a new aero diesel that is not based on an existing engine, I would neither use a V-type engine, nor liquid cooling nor a reduction gear nor 4-stroke...
I have flown a lot on the C421 and C404 and this is really what you want/need in that kind of aircraft! For passenger comfort, a geared engine is second best to a jet. Also in terms of efficiency, a large-diamter, slowly rotating propeller is much better. In all my time on these aircraft, I have never had any trouble with the reduction gears!
As for the liquid cooling, the lack thereof is one of the largest handicaps of the pressurised twins. You have to descend very early and very carefully in order to avoid shock-cooling of the air cooled engines. A very uneconomic way to operate this kind of aircraft, as it really should be flown as high as possible for as long as possible in order to take advantage of it's capabilities.
Four-stroke again is a tribute to noise requirements that are difficult to meet with such large engines otherwise.
And as for the V-layout, I can see nothing wrong with that either.
I think, this engine will be capable of something like 500 to 600 hp when fully developed and might even appeal as a retrofit for some turbine powered aircraft like the King Air 90.
I wish them luck!
Regards
Max
NB: Many years ago, when I was still operating 421s, there was a similar development from Orenda, but not diesel powered. We really considered fitting those engines to one of our 421 with high time engines, for the benefit of liquid cooling alone! But they never made it to certification.