At which point does porsche switch over to 2-stage system?

[flatsixcrazy]

Hello,
I am going to purchase a 73E that has been stripped off paints and I am looking to repaint it in its original color (Bahia red). I am thinking that the factory paint in 73 is single stage urethane by manufactured by glassurite?. At which point does Porsche switch over to 2 stage urethane paint system?. Thanks in advance for all your help. Andy