If the engine builder balanced it, he would have to have the balancer and the flywheel, or Torque converter for external balance no? Are you sure it was not internally balanced? You did not really answer or I missed it, is the bird a 6 pack bird? The 70 440-4 would be internally balanced engine.

Typically to run, you can use what you have to start the motor. Buddy who builds street and race motor hemi/440, uses a flywheel and automatic housing shell on the test stand.

Building a 440 currently for a show car, and it has 6 pack pistons, standard rods, and cast crank. Was figuring it would need the cast crank balance, but turns out it was pretty well balanced as is. Windup using normal balancer, and it will be internally balanced.

So you really need to ask the engine builder how it is balanced. If internal, you can use what ever you have to get the engine started on the stand.