If Gerald Ford is the GOP nominee, than Humphrey can associate Gerald Ford with Richard Nixon. I'm almost 100% positive that in 1976, most voters would've voted for Humphrey in 1968 if they could have a election do-over. Humphrey's best path to the White House is to go on the offensive, consistently attacking Ford for his pardon of Nixon. IIRC, Humphrey was popular with blue collar workers, and could sweep the industrial rust belt.
Here's a map of a close Humphrey election, fwiw:
HHH running in 1976 is no different than Al Gore running in 2008. Both had lost several times, but voters believed that they made the wrong choice in those elections, and would gladly have voted for the loser in those scenarios. Gore would've won against McCain if nominated.
I do agree that HHH would lose to Reagan, however.