68 318 or 79 360

You do not need a flexplate for the 360 unless you change the torque converter, the weights will be on the original torque converter. The 727 should be the same unless it is the short, very noticeably, 4x4 trans.

318 plusses: Probably a steel crank. short stroke, winds higher all things being equal; internally balanced; common motor mounts.

360 plusses: more torque, lower RPM all things being equal; better flowing heads; hardened exhaust seats, more prone to cracks.

Your choice. Can you hear them run? At the end of the day, what is your intended use? Remember Horse Power is King, torque is just part of the equation.