Greg I belive it would be a lot easyer to step up to the pay window with all the parts that work togather am not real familer with the 90 mustang set up but belive it is to wide & you would have trouble with the brake bias also. They make a cable setup as well as a hydraulic for the clutch.As for the roll bar belive you can weld brakets on with the fuel tank out. If you decide to take the Roll bar on measure 4 times
cut once (use a hole saw) that way when the 3rd leg doesn't quite fit you have something to fill around it.
PS call Finsh Line for the SS grommets around the Bars
LOL Ken