can i use my harmonic balancer from my 1986 305 z28 engine or my harmonic balancer from my 1988 z28 engine

 

A factory Vortec motor has a crank position sensor ring in front of the timing chain gear on the crank. It's about 1/8" thick, so GM shortened the hub on the balancer by the same amount. If you put on an earlier balancer the face of it will be out about 1/8" too far, and your pulleys won't line up properly.

If you remove that crank position sensor ring (i.e. you are not running a factory Vortec EFI system), then you can use an earlier pre-Vortec balancer.

 

thanks