i have a 1985 block and crank. i am going to get it balanced before i put it back together.what harmonic balancer do i use?? one for ext. or int. balance.can i use a early balancer from a 1969 of 1970. what flex plate for a c-4. the shop has to send the stuff out to get balanced and they want the flex plate and harmonic.i kinda want to stick to a stock set up.if i break one or the other and can just replace it with another stock piece and it won't screw up the balance job. need some help on this. thanks