The problem with fitment has three issues.
One, the thickness of a flex plate is less than a flywheel. This moves the engine closer or farther from the pump.
Two, the bolts for a flywheel will be too long for a flex plate.
Three, the locating dowel in the crank will be too long for a flex plate.
All these things can be modified to work with each other.
The difference will be pretty obvious.
GT
Sent from my SAMSUNG-SGH-I927 using SoCal Jet Boats mobile app