The HEI systems used two types of coils, but the canister type was not one of them. The external-coil HEI used a square-shaped coil with the laminations exposed, and a different wiring harness than the canister type coil. There are four low-voltage wire terminals on the external HEI coil, as opposed to only two primary terminals on the round, non-HEI units. They're definitely NOT interchangeable, as the primary circuit resistance is lower on a HEI unit. If you can find the distributor with the in-the-cap coil setup, its much easier to wire up, needing only a single, heavy (10 gauge) 12 volt wire from the ignition switch to the distributor to run. Be sure to bypass the built-in resistance wire from the switch to the original coil, BTW!
Jerry
