Thanks guys for the analysis, very cool. I am going to take my best digital camera to the shop tomorrow and get a good clean closeup picture of it, I should be able to tell which stamps are over what digits... i.e. which were stamped first. Ultimately, it's probably not that important, it just intrigued me...maybe I have a "lost ark" engine.
Also, I hope the damn thing has a 4" crank. I can confirm 100% this is not the original engine to the truck as the fellow I bought it from bought this engine from someone to replace the 351 that was in it when he bought it. Unfortunately, there was no history with the flathead engine he bought.
Cheers