I...bought the ST-2 because my Walmart's shelf had NO Motorcraft oil filters in stock.
That doesn't make sense. If they hadn't had any ST2s, would you have bought a Minwax stain can, stuffed it with rags, & used that???
There's the RIGHT part; and then there's everything else. I'd only buy the right part - PERIOD. If this store doesn't have it, try that store. Or order it online & wait for the RIGHT part. Another week of driving the old oil isn't nearly as bad for the engine as the WRONG filter could be.