The B-29 was usually equipped with 12 50cals (4 in fwd upper turret; 2 in fwd lower, rear upper, rear lower, and tail turrets) and one 20mm cannon in the tail. Excluding the 20mm cannon, it isn't any more heavily armed than the current B-17 we have. Its main advantages over the B-17 are its higher speed and much larger bomb load. As stated earlier, the B-29 was prone to engine fires. On the issue of inability to model it properly in AH, there are aircraft already included that benefit from the lack of RL flaws/problems (N1K engine unreliability & weak landing gear, P-38 turbo fires & prop runaway, etc).
PS, the B-17 gunship was the YB-40.