Windshield wiper question
 

What is the difference between wipers that are "hidden" and the other style, with regard to 68 GTO? Are the arms different dimensionally or...? I assumed they all were hidden on these A bodies...

Wiper arms before 68 were not hidden and sat on the lower edge of the wind shield when parked.
As on my 66 GTO.

wipers
 

This is the hidden wipers on a 75 Firebird. The hood comes up just shy of the windshield and the wipers tuck in underneath between the hood and the top of the cowl.

My question was more of wanting to know if there are differences in the actual arms...could hidden type be used on a non hidden car and vice versa?

Typically the entire wiper system components are different between non-hidden and hidden. The non-hidden arms have a bend in them so they stay above the hood edge. Driver's side wiper blade is also fixed and doesn't pivot like the hidden wiper system.

The arms are different. The hidden wiper system has an extra pivit arm on the driverside so it can park and still reman level. The wiper transmission will have an extra mount on it. The non hidden arms have a single arm. The chrome lower windhield trim is also different. The hidden chrome is bigger so when arms park below hood, they stay on the chrome.