A 1984 Lincoln Town Car has the right sized backing plates. The same 7/8 inch brake cylinders are used for 10 x 2 1/2 as on the 10 x 1 3/4. There is a difference in the offset for the bigger brakes so new drums are required. The backing plates from the 84 Lincoln bolt right up to the axle housing and have the same holes as the original backing plate for the wheel cylinder, parking brake cable, etc. Buy the hardware kit for the same backing plate.
Other Ford donors are
NOTE: Not all of these cars always came with 10 x 2 1/2 brakes, but some of each model listed above do. Also, when you go to buy parts, make sure the drums you buy are the right sized 5 lug bolt pattern.
The stock rear drum brake dimensions for a V-8 equipped Mustang measures 10 diameter x 1 3/4 wide.
The 57-59 Ford big-car rear end's drum brakes measures 11 x 2 wide.
For large 9-inch axle bearing housing applications only, the drum brake size can be increased to 11 x 2 1/4 by pirating a rear set of drums from a 65-67 Ford Galaxie. This will give a brake swept area increase of 1/2 inch over-all combined.
For even more stopping power, the addition of the 1960 model T-Bird rear drums will give you a dimension of 11 1/32 x 2 1/2