Ed,
All of the points above are good ones....the diaphragm in the fuel pump could have a leak and it would allow gas to pump into the
oil pan.
If you can not find out any specs on the Cam you can get a degree wheel, take off the valve covers, turn the engine over by hand and see where the intake/exhaust valves open and close. That would tell you very specifically how wild/mild the cam is.
One clean or one bad plug is more than likely an ignition problem.
Tony R.