just did a rock auto check on drums.
a listing for a 67 318 polara found a centric #12363005 drum, except hd/except wagon $54.79ea. [only 2 remaining]
in the info, it stated a friction surface width of 2.600", and no cooling fins.

looking up a raybestos application for the same polara with 11x2 1/2"drums, finds a brake surface width of 2.930", and has cooling fins.

i don't have any 11x2" drums, and the 11x2 1/2" drum sets i have are stashed in a place i would have to dig a while to get to, in order to measure the friction surface.
so take this info for what it's worth, and how much it cost you.