Have your parts guy check the replacement bearings and seals for both disc brakes and drum brakes on your Cougar. Recently I was packing the wheel bearings on my 70 Ranchero GT with drum brakes and power steering. I had purchased a set of spindles with backing plates and the dust covers from a friend off his 71 Ranchero GT with disc brakes and power steering, planning to do the conversion at some time down the way (I got the entire power brake assembly less the proportioning valve and his power steering ram and tie rod setup). He had a 351 Cleveland and I am pretty sure it had air conditioning. Mine is a 302 without air conditioning. The spindles are the same as far as bearings, both inner and outer measures the same with my mic. There is no reason to change spindles that I can see. I still have to buy rotors, caliper assemblies with pads and new brake lines (not to mention the parts necessary to mount the calipers to the backing plate. The prices from Rock Auto are the best I can find. The only down side is the factory brakes (and the Rock Auto replacements) only have a single piston vs the dual pistons of the kit, but it does not appear the aftermarket calipers will fit with factory 14 inch wheels. The stock ones do.
I also have another 70 Ranchero GT, 351 M code with air and factory disc brakes that will be getting the bearings packed or replaced soon. I plan on measuring them as well. It is a 70 that was built in November of 69, so I am sure that it will have 69 spindles on it. Somewhere I have a set of 73 Torino disk brake spindles that I can not find at present but when I do I will mic them also.