Ventral guns means belly guns - underneath the plane. In the Ju 88 this means the gondola.
I've got probably 50 photos of A-4's in books and for the upper rear armament they all show a pair of circular armor glass mounts, each having a single MG 81. Just like AH.
As for the MG FF, we must be talking about a different installation. The one I am talking about had the MG FF installed in the front of the gondola, right where the bombsight is located.
[This message has been edited by funked (edited 10-16-2000).]