Design is different between OEM MOPSR and aftermarket.

Motorad did buy Stant a few years back.

 

So, although Stant had one that fitted, Mopar commissioned them to make another one (&, presumably, paid for the R&D) but Stant carried on making the "old" one as well, Nope, can't figure at that logic, especially as, having looked at one of my spares (bearing the Pentastar logo) it looks like a perfectly standard 'stat to me, so the differences must be very subtle.