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Diamond engines, both A and B, were produced at least up to the war. They have a date cast into the block on the lower right front. Sometimes the dates are hard to decipher, but are there. Most, if not all had hard exhaust seats, all diamond castings were not the same, in thickness around the ports, etc. The diamond is a foundry mark so not produced on the Ford assemby line. The mark can be found on heads, bell housings, rear trans nounts, etc.