I've got one very similar to yours. (75 pound's) A guy told me it might be from the generator's used in copper mines out west?
Could also be marine. My dad sold diesel supplies back in the fifties, and he had lots of catalogs listing piston rings for bores as large as "96". When I asked him what they were used in, he told me all the really big stuff was marine. Given the number of diesel diesel powered ships scrapped after the Second World War, it would probably be the most common source. You'll probably never know unless you find some numbers on it, and that probably won't be of much help.
It is from a BIG-ASSED ENGINE. Kansas must have different laws about mail box posts than Ohio. I had a Buick torque tube cemented in the ground as a mail box post and the state made me replace it with a wooden post. They said if someone hit it, it would cause damage to their vehicle and probably also cause injury to the passengers. I told them if some sumbitch hit it I didn't care what damage it caused their vehicle. Guess who won that battle
My last mailbox before this one was hit by a kid riding in the back of a pickup truck with a baseball bat. I guess he didn't know it was made of 1/4" steel. SURPRISE! I'm thinking this is not marine (since it's in the middle of Kansas). I'm thinking it may be from a natural gas pumping station engine. I've been told that there is a pretty good portion of this below ground level. .bjb
I grew up in SE Iowa near one of these pumping stations. I recall some of the mechanics saying the pistons were several feet in diameter. Turbines are used today.
Marine Diesel , is my vote . We had one converted to run on Nat Gas . It was 10 ft high straight 8 , super charger and turbo charger . White was the brand . Tore it down many times , liners, pistons , rings , bearings , ground and lapped valves . Each cylinder had its own head and injector controls and temp gauges to monitor fuel mixture . This monster ran a compressor to compress natural gas from gas to a liquid in a process . I was 19 years old and it was my job to maintain a few of these monsters . Fun job , but hard labor intense . Everything was manual labor , just get a larger cheater bar . That is why I’m a broken train wreck in pain daily anymore .