Bedford Knocking Troubles

Gday,
I have a TK Bedford 1969, with a Bedford 330 Diesel, 4 speed box and a single speed rear end. She sat in a shed for 12 years idle before I bought her. Don't have any history other than she worked Sydney Markets and Newcastle Markets from the Central Coast 4 times a week. - No Mecanical history as gent was not exactly fluent in English although here for 50 years!!!!!!

I started to get a knock coming from within the motor, so i had the injectors cleaned and re-inserted the injectors, fired her up and she still was knocking

I was told to remove the head and get it serviced, which we found out 2 valves were dodgy and the head gasket was wrong. Back together again, got running without a hesistation, the knock reappeared but the sound seemed to be coming from the front of the motor. The motor is running sweet, there is not a miss in the exhaust, holding oil pressure well, and water temp is smooth (no fluxuation)

So we have just pulled the oil pan off to find small bits of piston and ring in the pan but they have come from the number 6 cylinder (rear of the motor)

I was wondering if anyone else has had this problem, or could explain the why the sound of the knock would be coming from the front, when the rear cylinder has the damage???
Would this be referred noise from vibration???? - No scoring in cylinders.
Any Help Much Appreciated