The Zoche is dead because its builder never intended to build it: it
was a venture capital scheme.

The certificated diesels being introduced are going to be more
expensive than a Lycoming, because they are going to be a premium
alternative to a Lyc or a lower priced alternative to a turbine for
countries where "aviation fuel" means kerosene and the car gas is pure
swill. Since Lyc and Continental will not produce an engine for car
gas under its issued ATC and many countries don't recognize the US
STC's, even if their car gas was usable, this makes economic sense.

There are several experimental-market engines like the Deltahawk out
there but I don't know if they are actually shipping. There are
conversions of general purpose production diesels such as the Isuzu
used in Dieselis, and if you speak French maybe you can get a set of
plans from them. They refuse to speak English, even though of course
if it weren't for us they'd be speaking German, but that's another
issue.