My HJ parts manual lists

NUT - WHEEL Hub Bolt
NUT ..................... Rally, Polycast Type Wheel ..............9939942......20

So, was this a part change sometime during the HJ range similar to the change in GTS facia's from silver to black. I always thought the nut change was so they could be used with both the Rally and Polycast rims but the Polycast rim was available from the start of the HJ run.

Thanks for the info Innuendo, I'm very happy to know the Black cap nut is probably correct for my early 75 HJ. Now just need to narrow down the change over date. Would be interesting to know what LH Torana parts catalogue lists.