
In all likelihood, yes. Feel free to email photos of the current situation to me if you'd like more input. tmiller@classicroof.com I will say this as well, there's a chance your old metal shingles are installed on spaced sheathing. Generally speaking, though, as tight as we make our homes today, I do not suggest metal installations over spaced sheathing on residential applications.
Another vote to remove them as well from me. You have 80 year old sheathing and solid decking will deliver a much more consist installation as well as address some of the venting part of the equation.
I have metal shingles on a roof (80 years old) and wish to install new metal roof. Do I need to remove the old metal shingles?