Hi Bryan. You may need points cleaned or adjusted or replaced. Check distributor shaft for side to side play. If the miss persisits, check compression. Also double check your firing order, make sure the plug wires are on right. Pertronix ignition is a great upgrade and easy to install. Mine took about 45 minutes, and the distributor stayed in the motor while I did it. Your 390 holds 5 quarts of oil with a filter replacement.

Hope this helps. Dave