Charon, look at the picture more carefully. The glass nose has 4 extra 50cal barrels protruding from it. This is not the standard glass nose, as you say
Medium Bomber Version: One flexible 0.50-inch machine gun in nose, 300 rounds. One fixed 0.50-inch machine gun in nose, 300 rounds. Beginning with B-25J-20, a second fixed 0.50-inch gun was added in the nose.http://www.csd.uwo.ca/~pettypi/elevon/baugher_us/b025-17.html
B-25J Mitchell: The most extensively produced B-25 variant, with deliveries totaling 4,318 aircraft, this 'Medium Level Bomber' had a crew of six with a glazed nose carrying one trainable and two fixed forward-firing 0.5 in (12.7 mm) Browning machine guns. The dorsal turret was moved further forward to a position just to the rear of the main cabin, and the first 150 aircraft were completed with provisions for a 2,000 lb bomb or torpedo. Many of the aircraft were later adapted with a 'solid' nose and armed with eight 50 cal Browning machine guns. Variants that were produced as conversions from B-25J standard included the CB-25J Mitchell utility transport and the VB-25J Mitchell staff transport.http://members.fortunecity.com/llium/history/warbirds/usa/b-25.html
...The B-25J was effectively the same as a B-25H, but with no 75 millimeter cannon and a different nose, or rather a pair of alternate noses. The first was a glass nose with one flexible and two fixed 12.7 millimeter Brownings, and the second was a "strafer" nose with eight 12.7 millimeter Brownings. The longer noses resulted in the B-25J returning to the length of the B-25C/D. In principle, the strafer nose could be fitted to earlier B-25 variants in the field. Other changes included reinstatement of the copilot position, giving the B-15J a six-man crew, and uprated P&W R-2600-29 engines...http://66.102.7.104/search?q=cache:5L_DDCItyzQJ:[url]www.vectorsite.net/avb25.html+B-25+nose+armament&hl=en&start=17[/url]There is also a cutaway of a J model here. It is a pre -20 with only the single fixed .50 fitted and the single flex .50.
