U.S. intelligence report and photographs of the Ju 88 night fighter ventral gondola armed with four 20mm guns, from Informational Intelligence Summary, No. 44-29, Office of the Assistant Chief of Air Staff, Intelligence, Washington, D.C., Sept. 20, 1944.
INCREASE IN NIGHT FIGHTER ARMAMENT OF THE JUNKERS 88
The previously-reported forward-firing of armament of the Ju 88 night fighter version was 3 x 7.9mm and 3 x 20mm guns. Two of the 20mm cannon were placed in a ventral gondola. In a night fighter recently captured in France this armament had been increased by the addition of two 20mm in a streamlined ventral gondola. Front and side views of the 4-cannon gondola appear as Figs. 6 and 7.
Was the Ju88G version. Not sure it ever had the 2 MGs.