They Rust in the UK They usually attract old people who need to be reborn bikers over rated and over here they are commonly known as a girls bike they are a statement on how small your penis could be marmite you either like them or hate them
They have a novelty value and are seen as "Real" Harleys by their fans, later EVO motors are much nicer and easier to live with unless you like holding spanners and not handlebars. They are from an era when to be a rider you had to be a mechanic. Not like many of the "wanna be" owners that play at being weekend outlaws today with their dealer serviced turn key and ignor bikes.
I'd buy one if it was real cheap. Don't compare them to a jap bike, Very different.
What do you want to know about old school "real" H.D.s????????
In general they had two wheels held apart by a frame and forks with an engine and gearbox in the middle making a whole unit called a motorcycle.
Now the sensible bit:- I rode a Shovelhead chop (engine tuned for 95bhp, which was a lot back then - with transmission beefed up to cope with that prodigious power) for 14 years. Rebuilt it about 10 times and it constantly needed fettling, though it was reliable and only left me stranded at the side of the road once after I'd used silicone gasket which blocked an oilway to the valve gear and it dropped a valve - own stupid fault. I had a strong attachment to that bike and when I had to sell it on it felt like hacking off my right arm. Go for an old Shovelhead if you want it to take over your life ( a bit like being committed to the woman you love). Don't waste your time and money if it's just a passing fad.