360 Mild Build Questions

Neutral balance the engine at a good shop with a digital balancer within at least 2 grams or less . Do it with a neutral balance damper. You'll thank yourself down the road when you need a converter or trans work. I have not seen one externally balanced engine balanced correctly. If they don't vibrate the car they are assumed OK.

If you don't want to spend the money on a Damper. Have it balanced with a after market 360 flex plate to run a neutral balance torque converter

If its a 4 speed car throw the external flywheel away and get a Neutral Damper and flywheel.