The quickest way I know how to check for a miss is to start at No. 1 spark plug wire. Disconnect the wire at the spark plug to see if engine dies any. If it does reconnect and move to the next plug wire. Complete left side first then move to right side. If you pull a wire and engine idle does't change, replace spark plug with a new one. If this does not help ground the spark plug wire to metal. If no arc swap out wire with another to see if you get fire. If still no fire check the under-side of cap. Look for a carbon trail from center black button (coil) to any of the eight terminals or if terminals are corroded. Replace the cap and rotor. If this does not fix the problem check out this: Mallory Ignition 8360M - Mallory Promaster Series Distributors - Overview - SummitRacing.com
. Call the order in by phone so you can tell the salesperson that you want the three wire dizzy. It also comes in a two wire model that will need an ignition box. Throw the GM HEI in the thrash.