FWIW, one source states,
"The Pahlavi regime’s claim that in 1949 there was an “attempt” on the life of the shah – after which the Tudeh was banned, repression was reinforced, and the Constitution was appended under anti-democratic conditions to increase the autocratic power of the shah – has never been questioned. In a detailed study of this issue I have, on the bases of irrefutable archival documents, demonstrated that the “attempt” was fake and stage-managed by the royal court in order to re-establish Reza Shah’s autocracy. See C. Chaqueri, The Shah’s first coup d’état,1949 (forthcoming)."
http://monderusse.revues.org/22?file=1
Unfortunately, I have not been able to find the "forthcoming" work online, and do not know what his evidence is for its thesis, but Chaqueri does seem to be a respectable historian, not a crackpot, being the editor of a Harvard Middle Eastern Monograph on *The Armenians of Iran* and author of *The Soviet Socialist Republic of Iran, 1920-1921* (Pittsburgh University Press 1994).