In the case of this 1972, it is going to have some serious mods to take the 3.8 engine with a monster air injection and a 6 speed.
1: stitch weld the tub.
2: reinforce the shock tower.
3: rinforce the jack points.
4: double the inner rocker panels.
5: weld in strut braces.
6. weld in section for power brakes.
7: remove rear tray and fab custom one.
8: remove rocker panel and fab stainless steel oil lines.
9: remove rain gutters for a slick look.
151: prepare for a tripple black paint.
201: polish to the highest shine...I want to see myself !!
Once the gaps and lines have been matched, it's all down hill from there.