I'm about to buy an HEI distibutor from my cousin for $30 it needs a new cap and rotor, but my question is if any will there be a performance gain and how much better is this then the Mallory dual point distributor that I have now?

They are more reliable. You may feel a performance gain depending on the condition of your old dual point distributor.

Dave

if both are in good condition the performance gain will depend on the timing curves of each. One thing is that you can run a wider plug gap with the HEI and the plugs will last longer. Don't forget to run straight 12V wire to the HEI, the resistance wire used with points must be bypassed.

If the HEI is "take out" it's likely the Mallory will have a better curve.