This bike belonged to a guy who died in a car crash. His brother inhereted it, and had no use for it anymore. But he wanted it to belong to someone who really appreciated the bike, and treat it with respect. I felt very honoured to be allowed to buy it.
The bike was almost original, and I had...
back in the days there was this hype to ride a Klein with 500 mm seatposts. 20" will do fine then, but I recommend a 21" for you.
Also, I would recommend 180 mm cranks.