Taking the 1975 quote out of context of the rest of the interview, it to be selling a lie.
Besides, it was his way of reversing it to the libertarians, first he tells them that they should embrace conservatism, and then he explains why they are misguided by refusing to do so.
No. It’s not out of context to any degree whatsoever. His words are as clear as a bell and you can’t change them at all. He simply defined libertarianism as the heart and soul of conservatism. There is nothing you can ever say that will change that clear statement. You are simply wrong.