Those are real nice if that bar is straight it’s a very good quality set
The plates are milled so they are true to their marked weight
Soak the plates in coke or white vinegar for a few days and it will take the rust off
Then dry them and either paint them or just rub some gun solvent on them and wipe off the excess
Use some penetrating oil on the bar end set screws so you don’t strip them, let it soak in for a few days
Then take them off and clean the bar with some hoppes 9 gun solvent let it soak on them for a few days the wipe it dry
I have eight 400lb york sets that vintage and Ive had them since the early 70s they are still in perfect shape