Image, caption and text from Martin Aircraft 1909-1960 by John R Breihan/Stan Piet/Roger S Mason, Narkiewicz//Thompson 1995. The text suggests the solid-nose ground-attack version and the G.R. VI were separate projects.
In 1942 and 1943 Martin suggested an anti-shipping version with a stretched fuselage to accomodate extra fuel tanks and an internal torpedo bay, a heavily-gunned solid-nose ground-attack version, and even a long-range fighter design. Late in 1943 Martin equipped two Mark Vs with nose radomes as prototypes for an A-30C/Baltimore VI G.R. maritime reconnaissance version. It was to no avail. The whole Model 187 program was cancelled abruptly in April 1944.
Baltimore FW289, a Baltimore V, was the prototype for the Mk VI G.R. maritime reconnaissance with nose radome, February 1944.