Harmonic Balancers

I run a Ati super damper on my 410 sb on the street works very well. Double groove alt pulley, 1970 water pump and crank pulley. Crank pulley was off 3/4 of an inch. Ordered a Cvf 67 to 69 crank pulley 3/4 in shorter and they lined up great! It came with one hole slotted already, so it was a bolt on. Some advice on the flat hex bolts that hold the the cover on the balancer lock tight them! If they loosen they will break! Ask me how I know!