Since there was a few questions on this, I thought I'd dig up some old photos.
The minitub process represented about six+ months work.
The inner minitub was easy.
Stretching the rear quarters, reshrinking the metal a few weeks
Blocking the quarter panels took ages, but was well worth the time.
Each step involved checking the progress. It involved setting up some halogen lights on an angle, then sheening the quarter with a spray of lightly soapy water, to make the quarter panel shiny.
There are a few important body lines on the quarter panel. The top ridge, is most important. Next the scallop where the scoop sits. Then the fender lip region. Then there is an additional line at the back of the rear quarter, where if you look closely, you can see a strip of masking tape. This technique was used everywhere on the car to sharpen all the body lines.
Then of course matching the fender extensions to the quarter panel, bumper and valance.
1st two pics are before pics
In the one photo, you can see there is about 15" from the inner wheel well to the outer lip.
I got a test 11x17" mustang rim, from a local tire company, to mockup for fitment and backspacing.
Brings back bodywork nightmares