If your doing a full restoration or need to replace your Mustang trunk lid because it's been damaged, there is a good possibility that you will need to realign the deck lid.
In most cases you will only need to align the trunk lid front to back and side to side, in some cases you may need to adjust the height of the deck so the body lines near the back window and quarter panels all line up nicely.
I'm doing a full restoration on this Pink Mustang and I've elected to leave the trunk hinges and tension bar installed; I would recommend that you do the same unless you want to deal with the aggravation of installing the tension rods.
Installing the Trunk Lid
I began my deck lid installation by removing the old trunk seal, installing the trunk latch striker and then mounting the lid to the hinges.
Install the quarter panel extensions
Next I take a general look at the overall fit, install the trunk latch and then mount the quarter panel extensions; the extensions also have to be lined up with the quarter panels and trunk lid.
There is a quarter panel extension seal available for 64-73 Mustang that you should install to make those body line adjustments, buy two sets; one for fit and body work stages and one for final assembly.
Aligning the Deck
There are four positions that can be adjusted to improve the alignment and fit of the deck lid on the Mustang, one of these is the trunk hinge that sets the deck height. In some cases an adjustment may not be required here but you should confirm that by temporarily installing a new trunk seal/weather strip; the new gasket may cause the deck to rise depending on its thickness.
Install the trunk seal so the narrow part of the V is inboard and the thicker part is outboard.
Here is the breakdown for the adjustment points and positioning:
Aligning the quarter panel extensions
Two parts on the classic Mustang that stand out the most when it comes to poor factory fit is the front fender extensions (head light buckets) and the rear quarter panel extensions. The quarter panel extensions typically line up pretty well on the sides of the quarter panel bit the fit at the top is poor.
The top edges of my extension sit a little high in some areas where they meet the top of the quarter panel so I've used a rat tail file to shave off some of the metal for a closer more inform contour fit with the quarter panels.
The final step is to smooth everything out with an orbital sander; now its time to remove the deck lid and prepare to strip it, seal it and install it again.