Physically different carbs. You can bolt the one onto the other, but there's enough stuff that's different that it's far from optimal. Easier to adapt a 273-318 BBD to a 225 than to go the other direction.
But all that aside, I don't think it should be leaking through the throttle shaft (seems only the driver side) during hot-soak engine shut-down / cool off. ?
Means the carburetor is percolating (boiling) after shutdown, and the throttle shaft bushings are worn or, in the case of thie "100% NEW NEW NEW NEW!" Chinese knockoff of a Carter BBD, it means you are seeing the poor quality of these things.
What year is your car?
And why are you running high-test gasoline? There's no advantage to it in a stock or near-stock 318; it's purely a money-waste.