Ignoramus14555 writes:

I am wondering, though, how come the four valves are so
close. I cannot imagine cylinder placement that would fit these
valves. For a diesel, we need 2 valves per cylinder, intake and
exhaust. If so, how could the cylinders be placed?

I think some 2-stroke diesels had four exhaust valves per
cylinder (as used in EMD locomotives, for example).
Intake was through ports at the bottom of the cylinder, blown by
a supercharger.

A four-stroke diesel would have two intake and two exhaust valves
per cylinder. I can't tell from the pictures, but you should be
able to see where the ports go.