I like that idea Jeff ---
But you wouldn't need the .5 ----
But the ADEN and DEFA didn't come about until after the Allies got hold of the Mauser MK.213 and from what I've read, the two cannon were direct copies of it. So until then it wouldn't have happened during the war. I have also read that Hispano did have a design for a 30mm along the lines of their 20mm during the late years of the war, maybe that would be a better train of thought.
I've got a couple of P-47N's in the stash (one part built), I think I'll build one with the 20mm as the discussion has gone ------