70RR. In process of restoring a non-AC heater box. Already ordered kit from member here

How do you restor the fiberglass box? I see YO sells a kit with cleaner and spray base and top coat... anyone use it? Is there something better etc...?

Also how do you reproduce the yellow part# on the metal plate?

68 Charger 383/ AT Green/Green VT
70 Roadrunner 383/4sp Purple/Black VT