I always wait to make permanent modifications until I'm pretty sure it's necessary. I think your port will be too big, but as you said, you can always tame it with an adj block. Take this as your first lesson that most "gunsmiths" don't know as much about these animals as they think they do...And most shops, and even manufacturers don't know the difference between an LR308 and an AR10. We're always learning and sharing in here. It usually takes mistakes to make discoveries.