I have no idea where Reddish Vale is.
The Waterdale stuff links in nicely with the Sustrans 6 route and the canal network around Little Lever. There are various bits that you can add to it. Hurst Woods, Moses Gate, Clifton Country Park, Nob End (snigger), Prestolee Road etc.
Get yourself on Google Earth or an OS and stitch a route together. You should be able to make up 20
Oh, well you should, let me know if you want a GPS track to follow! I’ll see what I can work out and maybe head on up that way sometime soon. Cheers