Relinquished effect on Facedown monsters?

Hey! I have a question about good old Relinquished we all remember from the old days.
It's a monster with 0 atk and def, and got an effect that can take an opponent's monster and make it to an equip spell card that gives Relinquished atk and def equal to the atk and def of the monster equipped.

And now for the actual question:
Can it's equipping effect be used on face down monsters? because it doesn't say on the card that it has to be a face-up monster. Also if this effect is working, does it still gain attack and def or is it still 0?

Yes you can take control of a facedown monster. It will gain nothing.

ok, thank you.

The monster will remain face-down when being treated as an Equip Spell card