That;s gonna be tough given the proximity of Russia though I figure it could be possible through proxies. If the US stood their ground and refused to help the UK with the Iranian coup, the UK probably would not have gone with it or tried something else and eventually, the US would have to step in. An Iran friendly with the USA and as a stable democracy would be a great help in Central Asia. I dont have much clue in Afghanistan though I'm wondering if they'd be better off as part of Iran.
As for Pakistan, really not sure given the political quagmire on splitting them up from India (probably wasn't a good idea.) If the Indian subcontinent remained whole though, then with this bigger Iran, the US had someone that could help influence Central Asia though it would look like or such is difficult to tell.