I looked up the part and the basic number for the bezel is 14528 for the single switch. (14527 seems to be the one for the 4 and 5 ganged switch)
For Full Sized Mercury in 69 the part is C9AZ-14528-A and for the Montego and Cougar lines the part number is C8AZ-14528-B
When I check the Ford part book I see the same part numbers for the Full sized and the mid-sized and Mustang. There is a confusing duplication for the mid-sized line showing a C8AZ-14528-A for 69 as well.
Lincolns, Marks and Thunderbirds seem to take different numbers.
I think you are safe to use a full sized Ford as a donor if you are working on a full sized Merc and to source from a mid-sized Ford or Mustang if you are working on a Montego or Cougar.
There is also a backing plate for the Montetgo and Cougar that doesn’t seem to appear on full sized cars. The part number is C8AZ-14523-A for both Ford and Mercury