Still need the magnum flexplate?

If I have the 5.9 Magnum serpentine Harmonic Balancer,do I need the Magnum flexplate also,or does the balancer provide the balance for the engine?
If I was to go with LA style belt set up will the 360 LA balancer work on the Magnum?
Talked to previous owner and he was under the impression the LA 360 balancer and 318 flexplate were enough.