It's a Mustang II what did you expect

Seriously, you picked a hatch back,T -Top car that has a huge amount of body flex. Even just my Hatch back (non T-Top car) Cobra II was a nighmare. Here are some things that should get you started.

Try to tighten up the body flex as much as possible. If you haven't already, re-install the unbder the hood T-Top braces. If they won't fit around the tunnel ram make some (check the engine compartment of my white coupe in my photo gallery, it shows a set I made for mine.

SuB-Frame connectors (they show up new on E Bay) will also go a long way in helping plus will help the car launch harder.

Get as much vibration out of the car as possible. A big one is out of ballance tires.

Next check the the door hinge pins, if they are loose, put new bushings in. Also chect the door striker bolts. They are supposed to have a plastic sleeve around the shaft where the latch hooks. If they are gone replace the striker pins.

Unless you already have, install new weather stripping on the doors, hatch and T Tops. A big squeek on the hatch can come from the hatch shifting back and forth and the latch rubbing on the U shaped hook it latches to.

The dashes on these cars are also a big problem with squeeks and rattles. Make sure all the dash screws are in place and tight. Also remove the top to the dash (There are screws under the foward lip of the dash pad, and should be a couple in the defroster vents. If the car has AC make sure the ducts are tight and look for anything that can feel loose (some thin foam can work wonders in seperating ratteling parts. Make sure the speaker mount is in place, as it also secures the top of the dash and keeps it from moving.

Finally remove the door pannels, and look for loose componets. also check the little adjustable "rub blocks", (an adjustable bracket with a piece of rubber/insulation) are in place and snug against the window.

Once all thats done you should have narrowed it down to maybe just a couple that should be easier to find.