Boo I looked at that link and I don't think his engine is that old.... His is a 70's model.... The B model would be right before that production engine.....
Looks to me like a 60000 series Briggs build in the late 60’s or early 70’s. Horsepower 3.5 or 5. Not that old, I actually worked on one very similar last week mount on a rototiller.
Rivet's ... The main reason I myself didn't say a 60000 series is because the choke is a dead giveaway.... The 60000 chokes go sideways instead of up and down....
That bigger tank also tells a story.... If they haven;t been changed of course...........
You are right, but that carb and tank can be used on the 60000, 80000, and 90000 series engines. It was one way we used to increase hp on the 3.5 hp engines. That was before we would sand heads, punch jets, and restrict airhorns to increase power. Even built one of these. https://m.youtube.com/watch?v=AMsXKkIuaPg