SPARK: Make sure all of your plug wires are good. If you don't know how to properly setup the dwell on a dual point, put in a temporary genuine Mopar electronic ignition and distributor. Should only take a few minutes if you setup an add-on electronic harness, that plugs into your 2 ballast resistor leads.
FUEL: Make sure that you aren't running low on Fuel Pressure >4000 rpm. Does it feel like it's running out of gas?
Do you have your initial timing set?
Are you sure that it isn't just pinging under load?