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There are now four books on English (five if you count Kasparov's MY GREAT PREDECESSORS) which deal with Leonid Stein: STEIN MOVE BY MOVE has been published by Everyman, written by a master whose previous work is the excellent MBM book on Petrosian.
All four books are worth having, but if you really want to know about his life and have some games, Gufeld remains the one.
But for thorough analysis, get the STEIN MBM.
Stein is put into context with Kasparov and Tal in the GREAT ATTACKERS book.
I have all four, even the Keene book is significant, if for no other reason than that it was the first treatment in English of a player who was highly regarded by Bobby. (Bobby also thought Petrosian to be the strongest player by far of the "Russians" in the early sixties.)
I think that Stein would have been a great opponent for Bobby: probably would have had a better chance in 1975 against him than Karpov would have. But we'll never know.
BTW, the match between Stein and Bobby was arranged during the Chess Olympiad in Havana. Castro was all for it, and agreed to host immediately after the conclusion of the Olympiad. But the USSR Championship was scheduled to begin shortly after that; and as it was being treated as a zonal tournament to qualify for the world championship cycle, Stein had to back out of the match.
I've read the Crouch book, and the Gufeld one is on my list of books I'd like the read this year.