I think Walt could have an effect on politics, maybe he lobby's for a different candidate in 1980.Neither do I. If you ask me, the presidents should remain the same as OTL until after Bill Clinton. If they change at all.
After all, the way I see it, this should mostly focus on the results of Walt living longer.
I think Nessie will be made and released for Spring 1977 for starters, everything else I'm not so sure.Oldnavy ever heard of unfhisehd movie. As the name suggest it has information on unfinished movies. I feel that it would be a good resoursce for you. Heres a link .https://cancelled-movies.fandom.com/wiki/Cancelled_Movies_Wiki