^ You could stretch that to YM 1985 - after that, the body shape changed (bootlid, bonnet, windscreen sill panel, etc).
Have had to look closely at this issue myself due to the requirements of Project Rudie, which is a loooong way off from being done.
Front guards can be sourced from 75-80 models. Most 81+ OZ market cars went to the bigger indicator lens aperture in the guards, but US didn't see that change till 85 IIRC.
5-panel tail-light rear beaver panels weren't often seen in OZ market 244s after 83, so you may have to use a rear beaver panel for 6-panel rear tails and patch up the extra holes. Or use 6-panel tails, which the 242 Turbos did.
Floor pan panels didn't change much AFAIK from 79 to 85, although you could use a 75-78 front floor pan cut in a 79 without too much of a stretch (they added an extra body plug in 79+ front pan panels)
Your 242GT may or may not have had "butt cheeks" (spare wheel wells on each side between the body members in the boot and the rear quarter panels) but all 244s did, so finding flat panels back there in a GT isn't unusual.
At the rear of the rear wheel arch, there is a joint which joins the inner wheel arch to the outer wheel arch and to the rear quarter panel, these are the most common places for all 240s to rust. If you can find a wreck with that triple joint intact, it's worth Sawzall'ing it out and reusing it.
The 242 lower 'B' pillars - a common rust point near the joint on the upper sill - are unique to 2-doors, so there's no easy way 'round that without fabrication and creativity.