I have never see any advertising for Oliver 4 & 6 cylinder engines used in marine applications.
FYI, The June 1. 1959 Oliver Power Unit price list show those engines. They are called "Oliver Boat Diesel Engines". The factory codes are as follows:
Model 166 engine is code 62 009
Model 177 engine is code 72 009
Model 188 engine is code 82 009
Model 199 engine is code 92 009
Extra add on equipment consists of a special insrument and electrial panel, governor control, tachourmeter, and engine front support. There ia also a listings for reverse gears and reduction gears for both the same as the engine rotation or in opposite of the engine rotation.