You need to be at least level 15 to begin this quest and should come with nightshade as an offering.
Glitched the ebony blade quest with the wooden plate thing. This is a known bug and has been noted at the UESP Wiki's 'Ebony Blade' article and has been reported in the Unofficial Skyrim Patch's bug tracker.
This post features the build of the Ebony Blade from The Elder Scrolls V: Skyrim. Both versions of the Ebony Blade can be placed upon a weapon rack, but neither will stay there.This may result in the loss of the blade when it falls off into unreachable areas. I know there is 17 daedric artifacts but maybe some of them don't count idk. So again, reverting it to it's original state is really questionable.
For the Khajit holding the Ebony Blade, I took the screenshot from a build known as the Regenerator Build.
Damage and reach are now on par with an Ebony Great Sword and it can be tempered with appropriate perks and materials.