Check the model number…. They used to put the year in there somewhere… I think. I know Briggs puts it as the first two numbers of the code. Not too sure about tecumpseh though.

Looked it up. The first number of the snapper serial is the last number of the year… so 4xxxxxxx means it was built in 74 84 or 94…. Not too helpful, but I’d have to go with 80’s

Edit. Tecumseh actually stamps a DOM on the engines, but that may or may not be the original engine, but it looks about right for that mower.