A Body firewall differences 68-70?

When did the firewalls in A bodies change ? I know 70 up has two indents or reinforcement ditches on the left and right top meeting the cowl. I have seen some 69s with them and some 69s without ,is this a mid year change ? Was there any 68s with these ?

Do you have any pictures of what you're talking about? Here's a picture of the firewall on my 68 convertible.

to the top left and right of the A shape,your 68 does not have them.

They changed every year until late 69. In the summer of 69 the final design for the 70 was completed. You will also find lower core supports with tabs for the upcoming Duster valance, I have seen quite a few of them on original cars. The 67 is completely different from the 68, then in 69 in changed again, then later in 69 like I said above. I have done extensive research on these 3 years but still have no idea why it changed so much. Also the 68 and 69 GTS hoods have different underhood bracing with a couple of crumple zones in the 69's.

Thanks Rhinodart for the info ,saw the 69 type marks on a 68 hemi dart and started to wonder if something was hokey.

original or a clone ? If original can you say REBODY ????

They said it was an original lo23 factory hemi dart. Looks now like a rebody or upper firewall cowl area replacement was done ,hopefuly they took lots of resto pics.