11" rear drum brakes.

Posted this in general and s/been here. Has any one had any experience with the 11" finned rear brake drums and using 14" stock Mopar rims. I am upgrading from 4"BC axles to 4.5"BC and have some 11"x2.5" backing plates I want to use as the old won't work with the new axles. The drums they came with are not finned and fit the 14" rims fine. I can't find new ones anywhere only the finned and are a larger outside diameter, I think they will just make it. Don't want to order them and be stuck with them if they won't fit. Any help would be appreciated.