Guild Wars 2

According to the wiki, you can combine 3 pieces of level 75 armor or higher with 1 weapon in the Mystic Forge. When I choose a weapon, it doesn’t allow me to choose the armor pieces. If I choose the armor first, then I cannot choose the weapon. If I place them all in there, the forge button is grayed out.

At this point in time, Precursor recipes do not exist, you may get one by chance by dropping lvl 70+ weapons of rare and above rarity into the mystic forge. However the chance of getting one is insanely small.