Reagan is going to have a very tough time in '76. As flawed as The Carter campaign was in the general election, they can very easily paint him out to be the second coming of Barry Goldwater and pull off a very decisive win. On top of that, Reagan would be the nominee of the President's party during a recession, and on top of that you have Watergate and Reagan can very easily be tied to Nixon just like Ford was but for different reasons.
However, if for whatever Reagan pulled off a miracle and won the GOP nomination and beat Carter in the general, 1980 TTL is going to be an even bigger disaster for the GOP than '80 OTL was for the Democrats. Reagan will have double digit inflation, a Soviet invasion of Afghanistan, and a revolution in Iran with an energy shortage just like Carter did. The hostage crisis may not happen, but all the other bad events of 1977-1980 are still going to happen, and Reagan, just like Carter will get blamed and lose the 1980 election. On top of that, Reagan will have voter fatigue to deal with as the GOP would've had the White House for 12 years in TTL, and 12 years of Vietnam, Watergate, energy shortages, and inflation is not going to help the GOP going into 1980.