Robert,
Your right the original Model T did not have an oil pump. Some folks added after market pumps and I think that this is what this fitting was for.
Any added pump was removed and the fitting blocked off before I got the vehicle.
There were hundreds of aftermarket oiling systems for Model T's
There's no oil pump on a T engine. This might have been a homebrewed attempt to get oil splashed from the flywheel and piped up to the #1 main bearing (which was oil starved most of the time).
