Sloppy steering

No, not "fully modified." Just rebuilt with good ball joints, tie rod ends, bushings. "We" drove these girls hundreds of thousands of miles. My old 70RR had over 140K on the clock when I sold it, with one front end rebuild. Admittedly, it had the best T bars the factory had, but nothing else was "modified" or aftermarket.

Even so, that old girl would handle circles around most any "family sedan" of the era

MY point is you don't need to "fully modify" anything, necessarily, to get it to go down the road, drive decent, and be perfectly safe at elevated highway speeds. Auto-X? That may be a different matter.