1959 Apache 283 Identification

[APatche]

I have a 1959 Chevy Apache 3100 with, what I'm told, is the original 283 engine. While attempting to decode/document everything about the truck, I came across these numbers on the front passengers side of the block; TIOIOD. I have searched everywhere and have asked in other forums with no success in decoding these numbers. Is anyone able to decode them or point me to a location where I can?