Balancer is what's weird, I have a 74 or 75 motor home block still together with a steel crank and the big rods, But a thinner beveled edge balancer that doesn't have the balance ring. I have a police 77 cast crank balancer, but I don't think I looks like the one you have either, I'll look tonite to double check. Only thing for sure is its a c-body block, not what's inside.
I checked, neither one I have look like yours.