The so called Humber expert (Alex Scott) gave some bum info, putting long reach spark plugs into a short reach side valve head. Said the spark being closer to the valve would give more power, what bollocks, more likely to foul the valve and with carbon forming on the exposed threads it would make the plugs hard to remove. He should have known that the head was cast iron, the 4 litre 6 cylinder engine was the same in the car and the Commer lorry