RE: Viking 44 ?????
"They are old and thirsty and loud and smokey."
The BEAUTY of DD is they can easily and cheaply be matched to the required HP.
While a semi plaining or true plaining boat will never be as efficient at low speeds (-20% or so) at least the engines can be reset for a bunch more efficiency if the boat will now be a displacement cruiser..
Injectors are about $35 each and can be owner installed , if one has ever adjusted the valves on a 6 cylinder Chevvy , and HAS the DD book, and a $35 tool.
Smoke comes from worn out or un-maintained engines , every brand.
If a DD stops smoking when warm (over 140F) the compression is good enough for another 5000 hours.
Most DD , if properly done will create 16 hp from a gallon of fuel.
In theory most tractor marinizations could make 18hp , tho most are set up for factory max RPM at full throttle , which reduces their efficiency at cruise to DD levels or even lower.
If a DD leaks , find a wrench to fix the gaskets.
If a DD smokes , decide WHY! and simply repair it .