Illinois fairly close to st louis mo
It would be best to get it on an alignment rack in order to get the correct tolerances set back in and to help stabilize the overall structure for the necessary repairs. That way you can be rest assured the car is true. Another suggestion, if it is possible along with a rack is to dismantle the car down to a shell. That way is is easier to set in temporary bracing, spot weld in new structural members and sheet steel without being encumbered or the worry of setting your car on fire. Attached is an image from the 1967 Ford factory service manual as to the correct measurements.
Have a look at the thread for my frame restoration project if you wish. You can see what might be in store once the carpet is up and the outer rockers are off.
https://cccforum.discoursehosting.net/t/mellow-yellow-69-convertible-frame-restoration/10997/10
Things ended well for me after an experienced welder spent weeks removing and replacing various metal.
Jacob, you need to post the town you live in and try to get someone from this site or who is knowledgeable with Cougars/ Mustangs to look at your car with you. There are structural issues/ rust problems that will require disassembly to determine extent of damage. From a couple of your pics the problems have been there for a while and were known to previous owner because of his comments on a shoddy repair. Probably fenders, hood and interior will need to come out that is why an experienced set of eyes can help as well as look at it safely. You might want to watch some “you tube” video of floor pan, torque box and cowl repair on a Cougar/Mustang to get an idea on what could be ahead.