Harmonic Balancer

[earnhardtgm3]

I need to put a harmonic balances on my 77 chev truck.The motor did not have one when I got it and had no timing cover.So I need to get a harmonic balancer and am going to be using this timing cover as I went to a hyd roller cam setup.
http://www.cloyes.com/HighPerformanc...S/Default.aspx
Do I need a 8 inch balancer?

Will also need timing pointer for timing cover as they are made in 6.75 or 8.00 in.
Looking at htis timing pointer.
http://www.tciauto.com/tc/chevy-smal...balancers.html