I hunted around but haven't found anything specific to adapting an FTA LNBF to a C-band co-rotor. Anybody have a link to a thread or a website showing details? Adapting a clamp can't be too difficult but how do you get the offset correct? Thanks.
Use a KU LNBF or KU Scalar/LNB designed for a prime focus dish. A regular LNBF is designed for a higher FD ratio and would only see a small portion of the reflector surface. Examples are the GEOSATpro SL1P or the Invacom ADF-120 scalar/feedhorn and n Inverto Black Pro C120 LNB.
The KU feed would be mounted on the horizontal axis of the dish. It could simply be strapped to the edge of the C-band scalar using a 1 3/4 pipe wall clamp or cut a slot in the C-band scalar to mount the KU feed as close as possible to the C-band feed and fabricate a clamp from a pipe hangar bracket to clamp the KU feed throat.