318 differences ??
Use the original vibration balancer for the engine, then put the 70 and later timing chain cover and water pump on.
Find TDC and make a new mark where the damper lines up on the new marks on the timing chain cover.
Then you're good to go...
PS: While changing the timing chain cover, get rid of the junk single row timing chain and install a good double roller timing chain. Like this one:
http://www.manciniracing.com/edelbrock4.html