Cast Crank main journal width… are these the proper bearings?

Are you sure It's a 77 model engine?
Look up a set of bearings on one of the car parts stores websites and click on the specs tab that usually comes up, and that will tell you. Then look up a 75 or older one and compare.
I left out 76 intentionally because that was the changeover year, a 76 motor could have either/or.