Shop around: Remeber, the key to a good HEI is the internal coil and the ignition module
Id try Summit of JEGS: They have some great deals on HEI that put out a good voltage. If you dont need the entire distributor, summit or JEGS also sells just the cap/coil/module all in one kit. Just install it in your current HEI distributor (should you already have one)
Remember, dont go cheap on spark plug wires either: Remember, spark is only as good as what actually produces AND how efficiantley it gets to the spark plug wires
If you need an entire distributor and what one you get, I recommend if you already have a vacum advance on your old one, get one that has vacum advance on it as well