Despite the physical design, or appearance or type of model engines, they are usually pretty well equally weighted along the axis
If you say ...''needing placement to the left [Port side], suggests the right [stdb side] of the engine is heavier in mass along the axis of the engine
It also suggests it is an engine [reciprocating to rotary motion, and not a motor [purely rotary motion]
If the engine were inverted and suspended, what is the resulting off-angle of the mass to the vertical?
What type of engine are you contemplating mounting?
Mounting is critical, however alignment is also an element in the setup and mounting and require an understanding of where the next step in a build
A machine type height, or vernier height gauge is an excellent method of accurately determining height, however not necessarily understanding moments of inertia, which apply to your question of rotary balance
Why not post some images of the engine & vessel in question
Derek