I've seen some people modify stock mustang quadrants...b ut i've also heard them complain too that it wasn't quite right. Search vintage mustangs site...I've seen some custom stuff there.
as for the fwa, I've seen people bolt it to an aluminum plate, which they then simply bolted to the fwa after they cut it to the right shape.
that cable is the fox length cable. It'll work fine with factory manifolds, but if you have headers, it's going to rub at #5 tube up front, that's why I suggested the longer 96+ adjustable cable or oem cable (the adj cable is a little longer for the mustang steve quadrant)
the quadrant can be done, and fabbed up, but don't cheap out if your fabrication skills aren't 100% and wind up with some hokey ****. I went with the mustangsteve quadrant, his fwa, and even his roller bearing assembly and the 96+ cable. In the end, I have less than $300 into it, but that includes the welding work and roller bearing pedal assembly....
the quadrant from mustang steve
and his roller bearing setup
I wanted to do this cheaply but do it right and never have to look back, and I have a real solid setup now