Found the problem. The intake valve seat on #7 came loose and turned enough to prevent the valve from closing. Exhaust valve was okay. Turns out the head was burned between the intake and exhaust valve on #6 enough to prevent it from firing at idle but picked up at about 1k rpm. Bought another head, had both heads rebuilt, new valves, 8 new seats, etc. New main and rod bearings, timing chain/gears, oil pump, etc. Put headers on it and stuck it back in.
Runs great but now have to replace/repair the oil pan. I brazed a 1-inch diameter copper extension tube to the rear of the oil pan to make oil changes less of a mess. The oil pan has the drain plug on the side which is directly over the front cross member and creates a terrible mess when changing oil. The brazed joint, although certain more than adequate, seems to have shaken enough to cause a leak since the drain tube is about 5-inches long. Got to pull the pan and either find one with the drain plug at the rear (where it should be) or wire-weld a steel tube in place with a "V" support bracket. If anyone knows where to find an oil pan for a 390 with the drain plug at the rear I would be most appreciative. Tks guys for the input. Another one for the frontal lobe storehouse.