So I never got the clear answer out of all of this. Does GM assemble the long blocks to Mercruiser specs? Or does Mercruiser buy individual components such as cranks, pistons and blocks and assemble them themselves.
I'm assuming that the electrical and fuel systems are all Mercruiser.
GM assembles the motors (longblocks). I believe that the entire engine is assembled by GM, including the accessories.
Volvo and Merc longblocks are identical, they just have different dressings such as manifolds, ECU's, etc.
The marine motors do have different internals than the other motors.