I dont think it should have the option for 8x20mm guns! There should be 2 options for 6x20 one of those being the gondola but there was a 1 of special permission required 8 gun version and only Rudi Dassow flew this plane. He disliked the BK5 so much that he requested permission to outfit his plane.
I've read it was so effective that they began producing it as a kit as well. That is why his setup has the "bulge" underneath -- this is the panel normally associated with the BK5. I still wonder if the real 4x20mm installation was smooth or not.
There is some debate as to whether the 8x setup meant 8x20mm (using a gondola) or is a misunderstanding of 8xGUNS total (counting the 2x MG131). However, I did a profile comparison of the gondola placement superimposed over the 4x installation, and it doesn't seem like it's in the way much.
It's the same with the 110G. You never carried the gondolas with the wing bombs. You never carried 30mms with the gondolas. The gondolas were there after the 4x7mm were removed to bolster forward firepower, but weren't used once the mk108s were installed. Yet we still have it. The loadout by itself is historically proper, but how we mix and match them is up to us (and HTC has explained they won't limit our mixing of historical loadouts as per discussions with the P51 rkts/bombs issue).
Thus it stands to reason if HTC does add it, you could very well make an 8x20mm setup, in-game. Whether the loadouts allow this is more a matter of their personal choice, rather than them intentionally limiting us, I think. Depends on if they have to cut back on loadouts or are just doing some of the basic options or what.