Many doubts come because the best seasons for 800m were 40 years ago, and current athletic fans don't have historical memory of the past.
At the end of 1985, we have already 5 athletes under 1'43" :
Coe 1'41"73, Cruz 1'41"77, Sammy Koskei 1'42"28, Johnny Gray 1'42"60 and Cram 1'42"88.
Coached by my friend Gianni Ghidini (they lived for 6 months per year in Bussolengo, near Verona, in Italy), at the beginning of 2000 years there were Wilfred Bungei 1'42"34 (2002), Gregory Konchellah (Yusuf Kamal) 1'42"79, William Yampoy 1'42"91, and I know all these performances were achieved by athletes in absolutely clean way. There were not special shoes, also the tracks were not like today.
So, we can say that short distances (800 - 1500m) for men didn't improve, since the same athletes of 40 years ago, with the same training methodology, could still now be able to win Olympic and to better WR.
The same didn't happen in longer distances : the improvement in 5000, 10000 and Marathon in the last 40 years was very big, and we can say the training method changed dramatically.
I don't see any reason for thinking that athletes able today to achieve the same performances of 40 years ago must use doping, while the athletes of 40 years ago were clean (at least, of sure they didn't use EPO that still didn't exist).