[Jim Brierley]

The diamond is a foundry mark, most, if not all were made after regular production, up to the war years. All were not the same, I have one diamond B block that was extremely thin in #3 exhaust port, another was ported to 1 3/4" and was still serviceable. The mark was A & B blocks, heads bell housings and on rear bearing (transmission) retainers and probably more??? They came with no serial number from the factory, most were used commercially. Were they better? They were newer, and most had exhaust seat inserts.