My titanium '89 has a dealer-installed ASC moonroof also. According to the stickers placed in the glovebox by the dealer, it was installed about 3 days after the car was delivered. Mine also doesn't have an access opening for the motor. And like yours, mine also has a crappy headliner job. It looks like they cut away most of the factory headliner board, and just streched cloth from panel to panel like a drum head. Trouble is of course, after all this time, it's saggy and loose.
My planned fix is to incorporate a factory moonroof headliner. The problem is, the factory moonroof (and hence opening) is larger than the ASC unit.
My work-around for this is to use a portion of a non-moonroof headliner as a donor. First, remove the rear seat, interior quarter panels, "A" post mouldings, and the bad headliner. Next, I'll cut the front half of the non-moonroof headliner to cover the area of the ASC moonroof opening, plus a margin of approx. 3" all the way around. I'll tape this into position temporarily and trace the opening perimeter from outside the car with the moonroof retracted. After removing from the car, I'll cut out the opening, then trim the outside to fit and clear any obstructions.
Next, temporarily affix the newly fabricated "plug" back into the car with tape. Then install the factory moonroof headliner into the car as normal. After making sure the headliner is positioned correctly, I'll place tape in the center of all four sides of the opening on the moonroof headliner, and also the "plug" that will now show around the margin of the original moonroof opening. Then make alignment marks on the tape with a sharpie. After removing the headliner and plug from the car, carefully align the previously made marks, affix the plug to the backside of the headliner with 3M spray adhesive, and allow to cure.
I haven't decided yet if I'll try and find a nice moonroof headliner, and leave the original foam and cloth intact, or just use what I can find, and strip the original cloth, and recover.
If I use existing headliners as-is, I'll buy some appropriate welting from an upholstery shop, and finish the raw edge of the factory moonroof opening with the welting. This will leave a reasonably finished looking edge where it steps down to the plug. The edges of the plug will be covered with the moonroof opening welting, and hidden under the headliner where it was previously glued.
Option 2 is to strip all headliner components, build up the headliner and plug as described above, then recover the entire assembly with new headliner material. This will yield a "one piece" look, and should look reasonably stock, even with the step-down around the moonroof opening. Another benefit of going this way is that I can refinish the sun shade in absolutely matching material.
Since I'll be using a factory headliner, the motor cover should approximate the location of the ACS motor fairly well. I'm sure it won't be off by more than an inch or so. This should be close enogh to service the motor in place, at a minimum. Even if the motor access doesn't work out well, at least I'll have fixed my saggy headliner in a way that looks reasonably factory.
I also plan to use a headliner from a later model T-Bird so that I can use the switch/dome light assembly that these cars used. The switch and bezel assembly from the earlier years are fragile and hard to find in decent condition. I picked up a switch/dome light assembly with bracket at the pick-n-pull for $5. They seem to be readily available. I'll just wire the ASC wiring into the factory switch, and the dome light wiring into the new dome light.
When I do this repair, I'll photodocument the process and post on the interior forum. I'll also describe what the problem areas are, and how well the whole job turned out.
Good luck with yours,
JD