[motoxlrg]

I have a Gen IV with a Bravo 1. I'm upgrading to a 540hp 496. Which flywheel and coupler would be best suited for this?

 

[BDMarine]

You didn't say if the 496 is a one or two piece rear main seal. One piece, you need a Gen V, two piece you need a Mark IV. The flywheel should have been balanced with the rotating assembly unless it is internally balanced. If it is internally balanced just get a neutral balance flywheel from GM P/N 3991469.
If it is not internally balanced, (which I doubt because the engine assembler would have included the flywheel..... hopefully) The GM p/n is 3993827.
Both those part numbers are for a Mark IV two piece rear main seal crankshaft.