I think you've got a good bit to go on here to start making a decision.
There's also enough on the car I'd at least try asking for reg/inspection records to document the 50k as being true...I've got a 160k, mostly summer driven, 1983 that was well cared for/garaged and looks similar condition wise, that pallex cloth on the seats wore well. Hard to saw with just a couple pics, but, it's surprising a 50k car doesn't keep things like original floor mats, underhood components, etc. (Oh, and carfax? My 376k mile suburban shows up as 87k original miles, and that regal shows I think around 26k. They're just not good for older cars)
The speedo mod, fuel pressure regulator, makes me wonder what else may have been more kidded before returning to stock. Two things, neither of which are uncommon or necessarily bad, to check are if a hot wire kit was added to the gas tank which is usually the sign of upgraded fuel pump (yes, improved drivability but not usually bothered with unless running bigger injectors/turbo/higher boost) and the waste gate rod on the turbo - in Stock form the rod is NOT adjustable, but a common mod is to cut the rod and use fitting to make it adjustable.
If the records don't show a timing chain upgrade, and you plan on driving it much, that's the first thing I'd do even before the wheels. The nylon teeth over steel gear just ask to break with age and heat, not a problem you want with it jumping time.
If the engine has been rebuilt, well, make sure it was done reputable - buick engines built by a chevy guy just don't last, they're a different animal.
Column/wheels shade may be off is they tried replacing a worn/cracked steering wheel with recovered/repop and paint didn't match so they redid both.
Original paint on this would be lacquer. If you see signs of clearcoat, it's a respray. Again, not necessarily bad, but, take into account on value.