"The Iranian mullahs had no interest in good relations with the US, and would have rejected the USSR."

What is the purpose of having a war with Iran. Punishment?????
A war's purpose must be to at least be at least to threaten the existance of a regime. If the Iranian's regime was threaten then they are going to accept outside assistance. USSR could assist Iran simply to thwart the US miltary.

"They hated both, but hated the US more. There is a fallacy that many nations or groups who are opposed to the US are just waiting for us to be nice the right way."

What I was suggesting was to deal with the mullahs by getting other mullahs to talk to them. In other words these guys take hostages all the time, they have a procedure of how to get hostages returned.
Now, the Mullahs aren't going to hold US hostages unless they want something from the US. And these guys are going to want to bargain. So, forgot about trying to get the hostages back in short period of time- it's not going to happen. Your bargaining should start with insisting the hostages are treated with respect- lavish respect. If these guys are religious, then they are going to follow their religious customs and laws. So this is all about rituals and honor and appearances.