Stock 273 4bbl intake question

I have the same intake, same hole for manifold vacuum but my boss hole is not drilled or tapped, underside is just a nub and no passages, same casting number.
Post 6
2536771 CAP 4BBL Intake Manifold Port Plug ?

Post a back side photo


More info with no answers.
Questions/Doubts Re: 1966 273 Commando Intake Manifold

My assumption was it was for some type of dry well temp sensor but I have nothing to go on for that assumption