Yeh, it is relevant. He thought you were setting up an early engine, at the time he posted that, you had not mentioned you are using a late water pump. These little details are important. MY question is, IS this balancer alleged to fit a SB or is it maybe for a B/ RB? Otherwise, I see no solution other than either using the early cover, or maybe cutting off the later cast tab and having the cover somehow plugged, not sure you can weld that "pot metal" alloy, or mill it flat and use a screwed on gasketed patch
The other possible issue with that big balancer is thickness front to rear. What is that going to do with the pulley situation?