My 90 Tbird LX 3.8L does not have 5x4.5 lug pattern. I went to install some later model wheels and found out the hard way. According to Auto Zone parts number search, the Tbird went to 4.5" pattern in 1991. That said, in order to get my new wheels to mount, do I just swap the hubs and rotors from a 91+, or is there more involved ?
One more thing, a friend of mine has a junk Cougar at his shop. Did the Cougar also switch to 4.5 in 1991 ? If so, can I just pull those hubs and rotors and be ok ?
No.
The MN-12 cars were ALL 5 x 4.25, from '89-'97.
And prior to 89 they were exclusively 4x4.25.
The MN12 cars (89-97 Cougar, Tbird, and the '93-'98 Mark VIII) used what is known as the Ford front wheel drive bolt pattern. Wheels from these cars will interchange with Taurus, sable, and such. No idea if the newer cars like Fusion and Focus and such will fit, or the newer Mustang wheels, for that matter.
You *could* weld, and then redrill the hubs, keep in mind you'd also need to redrill the rotors as well. These days you ought to be able to find a wheel you like, with the pattern you need and most manufacturers can make them in different amounts of backspacing.
Go here:
https://www.tccoa.com/threads/mustang-hub-swap-diy-as-of-2017.183418/
Good site as I used to frequent it alot when I had my '95 4.6L Bird.