[black69]

Mark Gillespie worked at Yenko and got the records of invoices and other data of where the blocks were cast, who machined them, etc. Lots of documentation. Somehow (hopefully his book will explain), he can decipher the stamped letters to actual production date and what type of block it should look like (say winters vs lockport foundry, etc).

Some of the blocks out there, never made it back to Don Yenko's shop from where they were made, but you have to read Mark's book on the details of that, and how it happened.