How do I tell if my 340 is internally balanced?

Factory cast cranks have the casting number on them with raised numbers. Their is a cast crank for the light rod 318 with no holes in the rod journals. Then there is a cast crank for the heavy rod 318. This crank has a hole in the front and rear journals like a 340 crank. Both 318 cranks are neutral balance. The late 72/73 340 crank is cast but it is externally balanced aka Detroit balanced. The 340 cast crank does not have the hole drilled all the way thru the front and rear journals. I would say he has a neutral balance 318 heavy rod cast crank. The number on it will verify what it is. It will still need balancing. The casting/ part number is raised on it also. Kim