How to place an assembly or part on an inclinded plane?

Hi, I created a new assembly, draw a centerline on the top place. Then, make a new inclined plane at an angle, say 45 degrees, to the top plane using Insert->Reference Geometry->Plane. Now, I have an inclined plane and I want to insert a previously created assembly or a part to this new assembly and place it on the inclined plane. I don't seem to be able to place it on the inclined plane. Could you please help?

SolidworksAssemblies