My guess is that it's still externally balanced. My reasoning is that it takes multiple pieces of heavy metal to internal balance a 428 crankshaft. I would think that would have been noted as it's $$$.
HOWEVER....
There's no way of knowing for 100% certainty unless you pull the
oil pan or contact the shop that built the engine. Unless it's a SCJ, all FE's use a zero balance harmonic balancer, so you can't tell by looking at the balancer. If it is a SCJ, there's a big fat hatchet weight hanging off of one side of the balancer spacer.
My vote is to call the shop. If they don't know, get it up on a stand, drop the pan and post pictures of the crank counterweights.