Goldwater wouldn't have agreed with Kasich on everything, but I doubt he would have backed Cruz for President over someone like Kasich. It's more than just policy positions. Cruz is extremely unprincipled, like you said, and possibly a bit too unprincipled for Barry to support him, even in a general election.
Plus it's not like Goldwater would have been that much closer to Cruz than Kasich on policy. The 1964 GOP platform was a long time ago, and Goldwater did shift a little later in life. Cruz is very much religious right. Not to mention Kasich isn't exactly a foreign policy dove or Russia-appeaser. He's a conservative Republican and not someone I would actually vote for, even if Kasich is perceived as a RINO because he's not mean enough.
Kasich ran as an economic moderate by the time he ran for president though. People have completely rewritten history and act like Trump was the only Republican who ran as an economic moderate that year which isn’t true . Kasich in 2015-16 supported the Medicaid Expansion, had a pretty moderate proposal on social security, and was pretty moderate on welfare issues as well . One of Kasich’s lines on the campaign trail was “Now, when you die and get to the meeting with St. Peter, he’s probably not going to ask you much about what you did about keeping government small,” Kasich said. “But he is going to ask you what you did for the poor. You better have a good answer.’”
https://slate.com/business/2015/08/republican-presidential-debate-john-kasich-gives-an-incredibly-stirring-defense-of-medicaid.htmlSo I don’t think Goldwater would really support him and I think a Goldwater in his prime would have run for President and have effectively been the conservative star during Obama’s 2nd term and unlike Cruz may have won the nomination as he’d have a much better relationship with the other candidates so they would be willing to coalesce the field around him .