if you're using a grey scale spec then just include the spec in the red channel and put the gloss in the blue or green of your spec/gloss textures. No need to use an alpha channel if you have others to spare. of course I guess this depends on the engine and guidelines..
Thanks for your input. I toned down the scratches in diffuse a lot then redid the whole specMap. In the spec map I removed all cloudes and used more even gradiants for spec. Render in game engine New spec map new diffuse map
But wouldn't I need to rerender using the Unity5 setup ie, Albedo,Spec,Gloss & Normal in order to get the correct spec map? If I just export my UE4 project to unity it exports the ue4 roughness and metal not the correct spec/gloss for Unity.
I cannot work out why the spec and cavity maps are inverted. The normal definitely is not and I cannot see any options to toggle inversion like in crazy bump.