The B-3 did not appear in any production plans. Originally it was to be similar to the B-2 but with the enlarged (45.5 m2) wing. Then the B-2 was proposed with the enlarged wing and DB 603L engines. It never happened, but this arrangement was subsequently designated the B-4, making the B-3 irrelevant.
The B-6 was to be equipped with the FuG 218 'Neptun' AI radar. The M15 and M16 aircraft were tested with various aerial arrays for the AI radar, wing aerials similar to those used with the SN-2 radar, horizontal dipoles and 'low resistance' wing aerials. There was a plan to develop internal aerials which was never realised. Other equipment fitted and tested at the Luftwaffe radio test centre (E-Stelle Werneuchen, near Berlin) included the FuG 120 'Bernhardine' blind landing system, FuG 125 'Hermine' VHF radio beacon receiver and FuG 350 'Naxos' which homed in on emissions from allied bombers. There is no solid evidence that any B-6s were completed before the end of the war.
Cheers
Steve