I found two very interesting pictures of a Messerschmitt Bf 109 K-prototype taken inside the Austrian Wiener Neustadt factory in a book named in Finnish "Luftwaffen koekoneet - Saksan ilmavoimien salaiset suunnitelmat ja prototyypit" (ISBN 952-5186-69-5) which has been translated from the English edition "Luftwaffe X-Planes - German Experimental and Prototype Planes of World War II" by Manfred Griehl. On pages 28 and 29 there are two pictures of a Bf 109 K-prototype taken from the front of the aircraft and from the side of the cockpit respectively. Unfortunately at the moment I can't upload any images, so please try to bear with me. What caught my attention is that the Erla Haube has a distinctive bulge instead of the normal straight line at the top. I've tried to recreate the image using a Wikipedia image of a Bf 109 K-6 and MS Paint. The red line represents the bulge I'm talking about:
The aircraft also doesn't have the Galland Panzer-headrest but a metallic-looking, relatively thin seat.
Has anybody seen something like what I'm describing? These two images are the only ones I have ever seen of such a configuration. On page 29 there's also a picture of a Bf 109 wing that has an MK 108 installed, so the aircraft might be a Bf 109 K-6, although I'm not sure if the picture is of the same prototype.
I'll try to upload the pictures later if I get my camera working again, but if you do have any information of such a configuration, please share.