Just installed Mac Longtubes 1 5/8 in my 89 fox convertible. Just a heads up for anyone getting ready to do this. I got the headers and h pipe for about 400 and to make them fit was another about 300, so in total will be about 700 bucks to make them fit. Also the instructions wont tell you that you will need to remove the starter to install the passenger side, also wont tell you that the passenger side will rest on the k member so you will need to either shimmy your motor mounts or but new, I went with energy suspension ones it raise it enough to keep it from resting on the k member but kept it low enough to let the hood close. Now the driver side was a pain it caught on the steering shaft so I replaced it with one from flaming river to correct, you will have to cut to fit. It was a pain but I got her done and anyone going through the same problems have any questions just ask. Also the h-pipe fits but you will have to line up each side them connect the h in the h-pipe and to get it to slide in I used a 2x4 and a BFhttp://www.stangnet.com/mustang-forums/newthread.php?do=newthread&f=20H. So to save yourself the heartache with the headers order a new steering shaft and new motor mounts and you should be good!
Heres some pics of them installed.
Heres some pics of them installed.