I've never heard of one for Mopars, but "clockable" just means you can rotate the outer part to clear obstacles.
It used to be a PITA to sell GM rebuilt alternators, because depending on what they fit---Bleck, Oldsmobubble, Cadiliac, Chevrolutz, Phoniac, and depending on what engine, you had to patiently explain to the customer how to take the thing apart and install the front half in a different spot in regards to the rear half, IE "clock"
If you look down this page you can see a couple of clock positions of the old Delco alternators
My attitude on this is that is "should never be allowed to happen." Header manufacturers should be forced---by lack of sales--to make headers that "fit what we have." We as owners should not have to "build" custom starters and other devices to put a set of damned headers on our cars!!!