Fox body rear end target width for narrowing?

[j-c-c]

Not a mustang guru, my sons 89 track only Fox body is a likely candidate for a TA/Big brake/ Big BC rear axle upgrade. Any body want to suggest a target/ballpark Flange to flange dimension on this 89 car? We haven't picked out wheels /tires, likely 18" custom or common sized, but we are upgrading, and don't see any serious fender flaring in the works, but liberal fender rolling is OK, and realize the bigger tire the better. I also understand factory tolerances, and we will have to measure for final decision, We are dumping the 8.8, and need to start dialing in axle Housings. OEM is 59.25"?, is this best?

[TheJDMan]

The measurement that actually matters is the "Wheel Mounting Surface" or WMS to WMS. This is the surface that the wheels are in contact with when installed on the axle and is directly relative to the wheels you will use. The optimal axle WMS to WMS measurement depends entirely on what wheels you will use. It is best to buy your preferred wheels/tires first, mock them up under the car and measure the actual WMS width you need. Wheel width and back space will effect the axle width.

[j-c-c]

Yes you are 100% correct, maybe I asked the wrong question. We plan on having a square tire set-up, and then taking my first question into account, what 18" max rim dimension is a good solution on the front, since that will determine my rear wheel width. The problem on the front at this time is not sure what aftermarket K member we might eventually move to, and then its resulting width we may end up with, for now I assume a stock K. Any real life numbers would still useful. Thanks.