Just going to add into this that I was a engine tester at Chevy engine plant Tonn,NY.A part of the test was a final balance of the engines while it was on the test stand.The wt on the flex plate(flywheel) was already welded on it on the assembly line and the testers would hammer tab wt's into the H/B'er.This was done on all SBC's and all BBC's too.