Observation - I see the bike was set up with Cantilever brakes originally, and someone's retrofitted V brakes.
You suggest it could be a 70's or 80's ATB. There was no such thing back then, and this looks like a late 90's at best or early 2000's design.
The plethora of mounts for mudguards/fenders and racks suggest it was more of an all-purpose bike. The front fork has a couple of holes, likely tapped, to take a front rack which is relatively uncommon, so this bike might have been aimed at the tourer or the shopper more than the sporty rider.
If its a "light" bike, then its likely made of Tange or other cro-molly steel instead of the low-end gaspipe steel tubes. This suggests it was a decent quality bike, and the Deore LX groupset was also a higher spec set of components.
LX came out in 1990 and continued for a number of years. It was aimed at the "trekking" market. If you look up the exact model number of the derailleurs then that will help give a better year range.
I see its really a triple crankset but someone's taken the biggest chainring off. This makes the front derailleur look really high and limits your faster speeds.
That the bike had canti brakes also supports "trekking" or touring as a purpose - at the time caliper brakes couldn't handle wider tyres as well, and cantis were seen as superior especially for touring.
As for a repaint? Unlikely, that colour was definitely in the 90s. I had a Raleigh Delmara with exactly the same shade of paint. If you give it a cut and polish, then wax the paint it will pop much better than that.
Loverly bike - you'll get a lot of enjoyment from it.