"is it equal to or mor or less than rebuilding say a 1974 plymouth duster?"

You will find it difficult to find parts for the F bodies. They were only built for 5 years and the sales dropped off quickly after their 1976 opening year. There is next to zero aftermarket parts being made, so a parts car is your only choice. Drivetrain is shared with every other RWd Mopar, but if smog checks are required in your area, these cars had a bunch of power robbing stuff to deal with. The front suspensions are terrible.
Besides that, they are great cars.