need help with replacing Harmonic Balancer

[67pro-street]

hi all, i have a 383 stroker that uses a crankshaft out of a 400 sbc (externaly balanced). my harmonic balancer cracked and i need to replace it. i was just wondering what all i need to buy in order to do the job correctly. i was talking to my uncle and he said that i will need a new balancer and a new seal as well as a new key. im not too sure what type of seal i should be getting and where exactly it goes. if someone could help me out, i would really appreciate it.

thanks,

67pro-street