My advice is not to try unless your DNA shows that Job was part of your
ancestry, or alternatively you need to dictate your first opus for
secretarial transcription. At any given road speed (if no change is made to
the primary gear ratios), the thrust or motive force available to you will be
equivalent to about 26 horsepower (compared to the original rating of 42).
That derives from a 28% reduction in available torque, and an additional 28%
reduction in hp because of the lower engine speed. As I have said too often
in the past, the key is torque, so consider the power loss to be roughly the
same as losing one cylinder in 4, or running the diesel with an air
conditioner on full bore.

On the other hand, everything that goes up must come down, so ... you'll make
up some of the time with the lack of engine braking going down the hill. You
could also fabricate a propane injector that just came on at full throttle,
but I predict melted pistons. Trade the trans for a regular diesel.

Frank Grunthaner