Is there any chance of the republican convention being unable to decide between Ford and Reagan? In that event, is it possible for the convention to nominate a "compromise candidate" who just so happens to be really unsuitable for the presidency, just so they can get it over and done with? Obviously this won't be clear when they're nominated, but a gaf-prone candidate who has the odd skeliton hidden away might have potential. If both camps see the nominee as a bad last-minute compromise, so much the better. Their's also the fact that noone would have voted for said candidate in the primaries-and if it looks like he has the nomination as a result of a rushed backroom deal (which it probably will), a Carter Landslide is probabal. I'd chuck in the odd rumour of a disagreement between the candidate, Ford and Reagan as well, thanks to a mildly dissbarriging comment from Ford or Reagan of the "if you give me 2 weeks, I might think of one." variety.
If either Ford or Reagan clinch the GOP nomination though, a Carter Landslide is dificult. I know Carter had a huge lead post convention, but Ford making up ground was pretty much inevitable, whether he was up against Carter, Yudal or RFK (though with the latter 2, it wouldn't be nearly as much as OTL).
Is there any chance of a strong third party bid happenning if either Ford or Reagan don't move quickly to patch things up? You could end up with Carter receiving more EVs as a result, 1912 style (though not to the same extent most probably).
Either Ford or Reagan selecting a running mate that looks good on paper, but has the potential for scandelless revelations as an October Surprise would be good, as would Carter picking someone other than Mondale, Scoop Jackson, Mo Yudal, Frank Church or John Glenn perhaps.
Combine a better running mate for Carter who's influencial enough to change his campaign for the better, with a broken GOP convention and a candidate that noone really wants-and you might have your recepie.
I don't think a Carter Landslide in itself changes anything after 1977, though the reasons that lead to his landslide might change enough during his 4 years to allow him a narrow victory in 1980, perhaps.