The one thing I'm hanging up on is "balanced with the rotating assembly". If the flex plate is balanced by itself, then dogdays is correct...any alone-balanced flex plate is OK with an internally balanced engine (they're both balanced neutrally).

However, if the engine's balance INCLUDES the balance on the flex plate it's a different story. Maybe I'm just hanging up on this since my big-rod motor is balanced WITH the flywheel & harmonic balancer, so I can't change flywheels without rebalancing. I had a shop check my flywheel balance & the machinist said it wobbled like crazy (not alone-balanced, so to speak...it's part of the engine balance).

Bottom line...dogdays sound knowledgeable in this area and it sounds like it would work fine. If it breaks (aka sounds like a rod knock), then it's not too tough to upgrade it later. I would suggest you ask your machinist if it is "alone-balanced" though just to be sure (aka neutral balanced separate from the engine).