I find it hard to believe that we can say absolutely - ALL Z/28's in 69 used the flat style stick.
I have pulled many a dipstick, and have found that both styles were used interchangeably throughout the model year.
The green tip, and the flat style were both being used in V8's at the same time with no particular reason.
Different vendors perhaps???
But unless the Z was different. and the flat chrome was used as a dress up item....
I would think they would be the same as all the other Flint V8's- both sticks used as was needed.
Both of those sticks have the same markings with just some slight variation here and there.
And I have seen many base V8 models with the flat style used.
So I really believe both sticks would be 100% correct.
I have even pulled some green tips in late 68 production impalas, Novas, and Chevelles.
All later replacements have the dimple in the handle.