I always liked them pointed "to the side" rather than "straight on" to the radiator, personally.
I think the "angle" may also be more of a cosmetic orientation. If the engine is on a stand at a car show, the casual visitor will not be prone to look right into the snorkel and see the air filter (or the flow deflector that Chrysler Corp used).
"FRONT" is there, near the clearance inset for the factory a/c compressor, to ensure things "look the right way", as the factory intended with the factory a/c option or otherwise. IF it is clocked much differently, it just does not look right. On some air cleaner parts, "FRONT" can also be found 180 degrees away from the front side of things, too. Buick used a sticker in the shape of an arrow on some applications, with the arrow pointing to the center of the radiator?
On our '66 Newport 383 2bbl, I slightly rotated the air cleaner so that the snorkel was aimed to get more of the air coming through the radiator. Possibly for a bit of "ram air" at highway speeds and a bit quicker warm-up in cold weather? I could tell no difference, but felt it should help a bit. Otherwise, it should have been getting normal under hood air.
Seems like a few car brands had air cleaner snorkels which were pointing to the center of the radiator? Those engines didn't have the flair of engines which had the "clocked" snorkels. Plus the front of the carburetor was also exposed. Carburetors were usually not a stylized part of the engine, nor the fuel lines going to it, BUT with a little spiffing-up, could look very good.
When the industry transitioned into dry filter air cleaner housing, the new air cleaners gave the OEMs an opportunity to stylize the under hood area better. Whether it be different colors for valve covers and air cleaners (Ford), size/number/configuration of snorkels, engine name ornamentation, or whatever, it was ALL about styling and "look" that was related to the level of the carline or any performance aspirations/indications for the particular engine.
Just some thoughts,
CBODY67