By Mark IV I'm assuming you mean first generation big block Chevy? And since it's externally balanced, it would have to be a 454, right?
As long as your crank pulley and engine coupler bolt to the auto pieces, there shouldn't be any issues using them. Mercruiser most likely just used what ever GM bolted to the engine for a balancer and flywheel when it was shipped from the GM engine plant to Merc.