Dipping vs blasting

The entire body went down into a vat of primer, and the boxed in areas have holes to allow the paint in and back out. So they should all be painted inside.

http://www.valiant.org/valiant/sinclair/sinclair-11.jpg

What year did they start that and on which models? I have bare metal under the 68 Dart and bare under the tank when I dropped it....