Ok, thanks for the measurement, wasn't sure if you had reached in and measured the dish, or just measured the sides of the "enclosure", it looks like it tapers "out", and is actually bigger than the dish.
I have no experience with the C/Ku voltage-controlled LNBFs, but there is a lot of documentation on this forum from people that have put them through the wringer.
The 3 common ones that I am aware of are the BSC-621 (some reports of problems with this one, others have done well with it), the GeoSat CK-1 (several good reports), and the new DMX741 (initial reports are promising, jury is still out).