Ignition problems.

If you decide to connect an HEI module: Whether using a 4 or 6 pin, connect the distributor pickup wires as per the diagrams, or the reluctor to rotor / cap timing will be wrong. This is called "rotor phasing" you can Google that

The HEI has a locator pin and if your mounting has no clearance hole for it, it must be broken/ filed off. Make certain the module is mounted flat on a flat surface and should have thermal compound for heat sink. Make sure both mounting holes are grounded.

You can bypass the ballast with an HEI, make sure the brown bypass wire is included when splicing. If it won't fire on the starter check that