Can I manually set the angle of an edge

I am modelling a Mayan pyramid, but I want the faces to be at exact 64º angles, how do I do this?

R [x,y,z] 64
That would be the key press sequence to get there. Choose one - x, y or z.
Object rotates around it’s Origin point (or 3dcursor, if that is set to be Pivot point). To get Origin on Plane’s edge in edit mode - select 1 edge or 2 vertices on both ends of the edge and Shift -S Cursor to selected. Tab to Object mode and on T-panel, Toolshelf, look for a button Origin.
Set it to be at 3dcursor. Now Plane will rotate around that edge.