Wasn’t Redwood the main alternative
Seems like Redwood was even being described as the candidate of the Tory Right
Yes, but if Major hadn't won a decisive enough victory* in the first round of voting, he intended to withdraw. The scenario is that Heseltine would have entered in a second round and beaten Redwood.
This is pretty much what happened in 1990. Thatcher beat Heseltine in the first round, but not decisively enough. So she withdrew, then Major entered the second round and beat Heseltine instead.
* He set a personal goal of 215 votes. He ended up exceeding that goal by only 3.