The 318/5.2 is an Internally balanced motor, the 360/5.9 is an Externally balanced motor.Are the older 318 (70's) and the later 5.2's have the same flywheel or will the older flywheel bolt up to a 5.2? What about 360's and later 5.9's?
273/318/5.2 and forged crank 340 are internally balanced can swap flywheels and balancers, cast crank 340 and 360/5.9 are externally balanced but each one needs a different flywheels and balancers.