This is the rear engine deck lid hinge typically used on CMC/FF/VS/early IM (although their has their logo cast into it) - it sounds like what you may be referring to. It is rough cast aluminum. It can be polished and dressed up with lightening holes.
Those models above use a flat rough cast aluminum (which also can be polished and lightened) -
Here's link to source - https://vintagespeedsterparts....iorparts.aspx?page=2
I learned a new word today: Frunk.