Thanks for all the help. Yesterday I ended up removing seat and going in that way. Took all my arm length and the longest ratchet extension I could find, but it worked.

Looks like when the latch is pushed down slightly past it's locking point (slamming the trunk, pushing down too hard) it sticks. It seems to be fine as long as I lightly close the trunk.

Funny surprise, in the trunk I found extra carpet that my dad must have bought at a flea market that matches the current carpet, and I found the original interior door panels, apparently my dad upgraded the door panels?

Anyone have a picture of what the '68 400 coupe door panels should look like?

Thanks again for all your suggestions, there was nothing like seeing daylight through the back when the trunk finally popped.