Hi Tony,
Here's what i know about this subject myself, and i hope it helps you.
I owm a '73 Mustang Convertible and i wanted to fit a Trunk/boot lid spoiler to the car.Over the the last year or so i've studied a lot of '71-'73 convertibles on line, and i've noticed that when you look behind the car, you will notice a lot of them have the trunk lid rising up on the right hand side above the quarter panel, whilst the left hand side tends to dip down slightly below the quarter panel.
Here's what i think is going on to create this problem. The problem lies with the torsion bar which has an uplifting force on the right side hinge which intern forces the lid to want to rise up on the right hand side. What forum members have said so far rings true, as these convertibles never came with factory spoilers, hence there was only one torsion bar offered to do the job of keeping the lid up.That set up work'd well and did the job.
When i bought my car, the lid protruded up on the right as well, and iv'e fixed that problem.On the left hand side hinge setup where the torsion bar is anchored to the three stay notches, which notch is yours anchored to at the moment? Top, middle or bottom? The standard position for the torsion rod was the middle notch position. That worked well.You mentioned your lid flies open with too much force i think.
Remember, less uplift force means the torsion rod goes to the lower notch, while max uplift goes to the top notch for the rod.You may have too much uplift force happening, causing the lid to rise dramatically to the right.The panel shop should have had no need to touch the torsion bar, even to take the lid off to work on it or relace it.
To get more technical, the trunk lid can only be adjusted and alighned in so many ways. The hinge bars themselves, have no adjustment where they are anchored to the body. The only adj you have is where the lid bolts onto the hinge bars. That gives you front/back and a little up/down adj. The lid lock assembly gives up/down and a litttle side/aside adj. If you want to move the lid from side to side at the back where the hinges are,you have to use push force on either side to coax the lid to move the direction you want.
Having said all that, it still wont solve the problem of the lid rising on the right.I came up with this idea of installing two hood adjustment rubbers inside the trunk lid area. These hood rubbers are fully adjustable, and do the job of forceably alighining the lid, so the lid sits at the right height on the left and right sides evenly.These adj hood stops don't affect the closing of the lid in any way and work like a dream. They are easily available from most Mustang outlets.
To install, mark out, position and drill holes behind lid.Using a tap & die set, tap a thread into the two holes. The threaded bolt ends of the stops simply screw into the holes and then you simply adjust the travel lenghts to suit how much rise and fall you want.Stop nuts come with the rubber stops and are used to lock in what adjustment height you have chosen.
This whole idea worked very well for me and solved my alighnment problem.If you install a spoiler, you can install another torsion rod going from right to left as well. I havn't done that as yet, as my lid just stays open on one rod, parked on a level surface.I will try moving my torsion rod up a norch and see if that gives me the lift i am chasing. One last thing.When i bought my car, the previous owner stuck a black striped decal across the back of the trunk. If you look at my photos i've posted on photobucket, you will now see how the alighnment was before, when the lid rose up to the right, and now that i have corrected that lid alighnment the decal is out of alighnment with the two quarter panel ends.
Hope all that helps Tony, and good luck!
Greg
http://s1295.photobucket.com/user/gregsladen/library/Mustang%20Trunk%20Alighnment?sort=3&page=1
