This, in fact, is not too different from the flat surface case, the difference lies only in the distribution of the force components along the '$x$ and $y$' components of velocity.
In the flat surface projection case, you have acceleration only along the vertical direction.
The given case can be converted to a non-inclined plane case by mentally rotating the system clockwise by $\alpha$ degrees. The only difference this would give you is in the two acceleration components, ($(a_x,a_y)=(-gsin\alpha,-gcos\alpha)$), which implies that both the $x$ and $y$ components of velocity would be affected by the gravitational force, unlike only the vertical component of velocity in the flat surface case. You can obtain a range expression like you did for the flat surface case.
(I've assumed that by range, you mean the distance traveled along the inclined plane.)