Just going to throw this out there.
It's difficult and expensive for crankshaft manufacturers to make molds and dies to produce properly designed end counterweights with enough mass in the correct location to balance the heavy internal components. This problem is compounded by increasing the stroke.
Increasing the stroke increases the distance between the center of rotation and the rod journals. Not only does this add mass to the crankshaft (where you don't want it), it moves the mass of piston and rod assembly further away, from the center of rotation, as well.
To counteract this, the mass of the counterweights need to be increased and/or moved further away from the center of rotation as well. Packaging constraints limit the size and shape of the counterweights, it needs to fit inside the engine block.
Externally balanced engines will have the required mass added to damper (balancer) and to the flexplate/flywheel. Internally balanced engines, requiring additional counterweight mass, will have Mallory metal (
https://en.m.wikipedia.org/wiki/Mallory_metal ) slugs installed in the counterweights, to provide the additional required mass.
Adding Mallory is very costly, therefore internally balancing this way is most often NOT done to engines that are not max-effort builds.
