First engine build question

Good for you to have that planned already! The good news is that you are going to lighter overall weights, and so the balance shop will take off the crankshaft weight by drilling into the end counterweights. They won't have add weight to the counterweights by drilling and installing heavy metal; that process would be more expensive.

And, your early 318 should have floating piston pins (retained in place by wire clips) and bushed connecting rods already. So that is a plus for you.