I made almost exactly the same construction. Within 1.5 hour I fetch my camera with the pictures and post a link to my prototype feed arrangement when I'm home.
I see L/Ku band implementation here: http://www.prutchi.com/2012/03/11/d-i-y-combined-l-band-23-cm-helical-feed-a... I wonder if this technique could be still valid for S band... I'm afraid that helix will be to small to fit LNB ?