Mostly all beech but some were made with Mahogany, though very few (sadly), no idea why would guess supply problems. Maybe they were from Sile Italy. The grain will look completely different from the plain ol beech, Mahogany being much more open and less dense than beech. I would guess Mk 3 or 4 mebbe, never seen a super with anything other than beech, but who knows?.
I seem to remember Nick Carter has one on his Airgun blog if you need to compare grain pattern.
HTH