I suspect that Reagan would have lost by LOTS
He would not be a serious candidate for the 1980 nomination
You are making the common mistake of underestimating Reagan. (This underestimation led Pat Brown to undermine George Christopher's campaign for governor of California in 1966 because Reagan would supposedly be a far easier candidate to defeat.) What I think a lot of people fail to understand is that Reagan never came across *to the voters* as an extremist, despite some of the things he said. He would seem very genial and reasonable in his TV debates with Carter.
I again urge you to read Geoffrey Kabaservice's *Rule and Ruin: The Downfall of Moderation and the Destruction of the Republican Party* in which he goes into detail on how after winning the gubernatorial nomination in 1966, Reagan was careful to be conciliatory to moderate Republicans: "In stark contrast to the gloating and purging that Goldwater's conservatives had indulged in two years earlier, Reagan's team made peace with the defeated moderates and asked them to join a unity ticket."
http://books.google.com/books?id=GJ9baqZLVIYC&pg=PA172 And of course Reagan could in 1976 point to eight years of having been governor of the largest state in the US, without, apparently having led it into either fascism or anarchy.
We should not forget that while in the general election, Reagan would have some disadvantages compared to Ford, he would have some advantages, too. After all, *he* hadn't pardoned Nixon or presided over the recession of 1974-5.
Does this mean I think Reagan would win? No. The GOP brand was tarnished after eight years of Republicans in the White House; however conciliatory Reagan tried to be, some Ford supporters would resent his successful primary challenge; and Carter's southernness and evangelical Christianity would eat into part of Reagan's natural constituency. But I do not see Reagan losing in a landslide, and it is even conceivable he might make it almost as close as Ford did, at least in the popular vote. (In the Electoral College, Reagan would probably lose worse than Ford, losing such Ford states as Michigan, New Jersey, and probably Illinois; OTOH, he had an excellent chance of carrying Texas, which Ford lost, as well as a couple of other southern states, like Mississippi and perhaps Louisiana.)
Once again, I really think that an understandable resentment of the Reagan cult which the Right has built up in a the past few decades leads some people to underestimate the man's political appeal.