fins&chrome- Since this is a repaint on an older car, I think there might be some uneven panels and the *possibility* of thin paint on certain edges and corners. Plus, while I'm always saying so straightforward this stuff is, there *is* a learning curve with the Flex.
So even with just #80 (and I suspect you are overestimating its aggressiveness by a wide margin), I'd probably tape places where an "oops!" is possible, but only while working on adjacent areas; the tape would keep things off potential trouble spots only until/after they're being worked on but they *would* still be machine polished.
Thin spots excepted, every place the polisher's pad will reach would end up getting machine polished, so there wouldn't be any areas for this particular concern. Tight spots that the polisher won't reach, yeah, do by hand. Ditto for any edges/corners where you suspect the paint might be thin. I'd rather you leave some marring on those spots than precipitate paintwork.
If the body is in such great shape that the panels and their edges are perfectly aligned, and the paintjob is so good that the paint on the edges is nice and thick, and if it were my car, then *I* wouldn't bother taping with the Flex/white/#80 combo. But those are some mighty big "if"s for a car of this vintage and if it were somebody else's car I'd probably tape (as described above) just to be on the safe side.
Don't use excessive amounts of product (gee, how many times have I said this

).
Also, I'm fairly experienced with this stuff, at least to the point where I usually know what's likely to happen before it actually does. When just getting started with machine polishing, it pays to err on the side of caution.