Only ever seen pictures of Vc's with the 4x20mm option.
1 maybe 2 Mk VIII's
IX's had a problem with heating the outer cannon on each wing.
Dan will correct me if I am wrong, but I don't think they flew operationally with 4x20mms, (or it's rarer that rocking horse doodoo).
4x20mm didn't become standard until the Mk.21 .
Oh - It's just a IX , no c designation. Only had IX and IXe, wing type was dropped after the V's, only change was to show an 'e' wing type.