Spinners with 50+ wickets who debuted in the 70s:The 70s or 90s, then the rest. The 70s really doesn't have a better spinner? And for the 90s, curious why Saeed isn't an option as an opener for 90s.
Australia: Kerry O'Keeffe, Ray Bright, Bruce Yardley, Jim Higgs
Eng: Phil Edmonds, Geoff Miller, John Emburey
India: Dilip Doshi, Shivlal Yadav
New Zealand: Stephen Boock
Pakistan: Wasim Raja, Iqbal Qasim, Abdul Qadir
(Wasim Raja was a batting all-rounder, but took 51 wickets in his 57 Tests so qualifies for the list).
Iqbal Qasim (28.11) has the best average of these, with the rest being 30+.