My dad has a GF-30 from that same era. I recently put a set of DR Veritas 12s on it, which usually are great with maple guitars. I found the mids were a little too loud and the higher notes on the B and E were a little quiet.
I would probably try D'Addario XT Phosphor Bronze 12s if it was me. They are rather bright and should add extra volume to those higher notes nicely (also a great choice to remove the boxy sound from smaller guitars).