[klemchen]

Hello,

the K-4 on the first picture is quite exceptional in having the round hatch above the footstep in fuselage section 2. On the G this hatch provided access to the main compass, but on that was moved on the K further backward into fuselage section 6, so the hatch in section 2 could be omitted.
Another feature specific to the K seems probably weakly discernible on the fuselage in the background of the third picture: On the F and G there was a large trapezoidal hatch with rounded corners on the starboard bottom of fuselage section 2. This was replaced on the K by a smaller circular hatch. The slightly darker round spot at the rear of bottom of section 2 might well be that hatch.

Regards,
klemchen