First I'd like to say the work being done here is amazing! I'm a little late on some of the earlier questions regarding the diesel engines "overhead" or valves and injectors etc. I spent several years rebuilding multiple types of diesel engines. From the looks of the photos and the videos, these diesel engines didn't have an "injection pump" per se' but rather a constant pressure diesel pump that provided fuel to the injector rack (lower tube running the length of the over head) which fed the injectors. The center push-rod, when lifted by the camshaft, activates the "rocker arm" and depresses the injector plunger which during it's downstroke both creates the high injection pressure and triggers the injection of the fuel through the injector nozzle. Fuel that is not injected during this cycle exits the injector assembly and is collected in the diesel return line (the upper tube running the length of the overhead.) The other two rocker arm assemblies are for (1) the air intake and (2) engine exhaust. If you look closely, you'll notice a considerably different center (injector) rocker arm and also as some of the pictures show, a much longer range of adjustment for the center push rod. This particular configuration (plunger activated injector) is still in use today in many commercial Cummins Diesel engines.
Many of the earlier diesel engines (not positive but likely in submarines as well) were two stroke rather than four stroke engines. These early diesels were often equipped with turbo chargers and intercoolers, however from the photos, it isn't obvious if they existed on the U-boat engines. Some reading I've done suggests that the engines were made by Man Diesel. Hopefully this info is helpful.
Matt
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