So I FINALLY replaced the battery on the Cougar (had to put tires on the wife's commuter, new battery in my truck, AND.....A rear master cylinder on my Harley). It was when I pulled the old battery and found it to be a group 58 (never really paid attention to the size as it was new when I got the car), which was more than a little smaller than the tray. So, I decided to do a little research and came up with the following:
The base model cars came with a group 22 (which is close in size to the 58 that was in it), with a Group 24 as an upgrade. The group 24 came standard in small block cars with a/c. And the big block cars either came with a group 27 (which also makes sense as you could get a 427, or 428 depending on the date of the build when you ordered a GT-E), or it was available as an upgrade to the cars that came with the group 24 battery (there is a little conflicting info on that one as like with everything else on the internet everyone chimes in until the real resto guy who has the real info shuts everyone down with accurate information).
Needless to say, I got the group 24 which fit the tray (mine is also a base model small block car with a/c so there is that).
I just thought it might be helpful to people who want the correct size, strength for their classic Cougar. Here are the measurements:
Group 22F-9 1/2"l x 6 7/8"w x 8 5/16"h
Group 24F- 10 3/4"l x 6 3/4"w x 9"h
Group 27F- 12 5/8"l x 6 3/4"w x 9"h
These are subject to a plus/minus due to manufacturers, but it will get you in the ball park if you find that the battery in your car does NOT fill the tray, as well as what your car came with providing the tray hasn't been replaced with a different size. Also, the "f" would notate a reverse polarity of the FoMoCo requirements which would also sometimes be notated by an "R" as in Group 24R, instead of 24F.