After many hours of research I found that only 4 to 6 K4's got 20 mm hub guns,these were preproduction airframes and only recieved the 20 mm because of a shortage of Mk108's.However all K4's were equipped to handle the 20 mm gondolas and some were shipped to squaddrons with the gondolas on.These were removed in the field as the pilots prefered the agility over the firepower.
That said there is no reason I can think of to not have the gondies as an option,hub 20mm no but gondies yes.
The 109's are suffering for a lack of hi alt models a G6as and a G14as would help and it seems to me they would require little work to make{but I'm not an expert}.