According to all the specs, you certainly should be using a
QPF-031 with the matching
ADF-120 horn, as Gabsphere commented, above.
However, with a 6' dish, if it's reasonably accurate, that's probably overkill, unless you are far outside the satellite footprint.
And by overkill, I mean both price and technical capability.
Here is
a more modestly priced solution for Ku-only, that looks good.
Haven't seen any members report on it, but since it's supposed to match your dish better than a
QPH-031 would, it may well outperform it.
... and for 1/5th the price of the QP
F and 120 horn.
Wonder if you have considered mounting a C-band and a Ku-band LNB side by side on the dish?
Lots of users do that, instead of trying to use one dual-band LNB .
Just another way to go.
We'd like to see some pictures of your dish and know what type it is.
Motorized 6'ers are not too common.
If you're using a Gospel brand C-band LNB, I'll assume you're in Canada, but if you'll give your location, maybe that'll give us some idea of satellite footprints for your neighborhood.