Wow, sorry I missed this one. Just going to be brief (as I can).

His reasons were: a patronising view of Latin America, a foreign policy predicated upon anti-communism, fear of Arbenz destabilising the area, pressure from regional allies to do something about Arbenz, and down from there.

I want to get the United Fruit angle out of the way at the outset. So, at the 202nd meeting of the NSC on June 17, 1954, John Foster Dulles and Allen Dulles basically torpedoed the idea that the coup was for or to protect United Fruit. The issue was that the Justice Department wanted to initiate an anti-trust case against United Fruit, but Foster thought if they did so, it would just prove Arbenz's claims correct. Nonetheless Dulles said that the case should go ahead and that at the very least the case would show Latin American nations that the U.S.'s foreign policy was not designed to protect the fruit company. Allen Dulles requested the Justice Department delay its case, for one month. After that month, Arbenz would be overthrown, then the case could go ahead. Interestingly, Allen Dulles stated that in all likelihood, Latin American nations would soon take steps against United Fruit that would do the Justice Department's job for it, speaking in positive terms.

If the Dulles brothers were so hell bent to protect former clients, it seems highly suspicious that they'd 1) Encourage an anti-trust suit, 2) Express relief at that anti-trust suit which appeared to be a slam dunk case, 3) Approvingly state that the United Fruit Company was about to have much of its land and power stripped from it by various nations in the region. Indeed, the CIA's own reports suggest Arbenz's land reforms were not a significant problem - agents in the area even suggested Armas take similar steps.

Other than the NSC meeting (which is in FRUS I'm sure), Cullather's "Secret History", and NSC 5419/1 (also likely FRUS).