The early bay hatch is slightly smaller height wise as far as i can remember, '68 might be different. My '64 panel has an early bay hatch fitted and the gap at the top does not look right, i have a replacement split hatch for it now.
I'll take measurements off them this evening including my '66 and get back to you.
EDIT: I have a rear hatch (totally rotten) from a '67 early bay so i'll put a tape on it too.