is there much of a differ. in harmonic balancers i need to get one for a 400 i seen there is diff. in sizes 8in and 6 3/4in will that change anything someone told me factory is better then aftermarket? is 1 co. better then another i had seen dorman has some cheep ones any help would be great i no very little about them thanks

 

since your running the 400 crank ,you have to run the 400 balancer and flywheel.these engines are externally balanced.the same goes for my 454.