Are the nuts ever an issue for street-driven 80s with stock tire sizes? I've only seen threads where they loosened on modified rigs off-road.
They are ABSOLUTELY an issue.
I bought my truck with 196K and very poor maintenance. I drove it like I stole it for 20K miles and one day at work, I happened to look under it and noticed that the right side had fewer studs than the left. So I crawled under it and there was only (1) stud remaining and it was on the verge of falling out. I tightened it the best I could with the limited tools and drove it home very slowly on non-populated streets.
The incredible thing is that it had been close since I bought the truck and the steering still felt as tight (or tighter) than all the non-LC solid axle 4x4's I had driven to date, so there was nothing "abnormal" about how it steered.
Turns out one had broken off, two had fallen out, and the fourth was barely screwed in and had wallowed out the threads a bit. I replace the three studs that were not broken off with new studs, nuts, cones, and flats and reassembled until I could get to my front axle rebuild. Then I went all out and replaced ALL of them with new (both sides) and carry three spares now.
I have read of a number of trucks that didn't catch it in time. Based on the design of the steering arms, when it comes off, you lose ALL control. The GM's you still control the LF wheel, but with these you lose it all. The RF wheel cocks out to the right, bends the end of the housing, locks up the wheel, and the LF wheel will go whichever way it decides at the time, and can determine where you go and if you end up in a roll.
That's why the comment is always "Check your nuts and lube your shafts!"