68 Dodge Dart

So today, me and my father went to a local paint shop to pick up some rust cleaner. The guys there recommended we use DX-520 instead of DX-579. I looked on the internet and found that we could use this after we prep the metal, but I'm not sure if we still need to use the DX-579. If anyone has experience or any knowledge regarding using these chemicals please help.

once again, its greatly appreciated.

Kevo