The aircraft is 42-24441 modified under Projetc S68 and had those two Emerson Model 136 jowl barbettes each with a 0.5" MG. But it also had the GE remote controlled turrets replaced with manned Martin turrets in the upper positions and manned Sperry A-2 ball turret in the lower forward position and a similar modified A-13 ball turret in the lower aft position. The waist blisters were replaced with manned flexible 0.5" MG. The above photo is one of a series from the Boeing archives dated to Aug - Oct 1944. See Detail & Scale Vol 10 B-29 Superfortress Part 1.
This aircraft is featured in Boeing Aircraft Since 1916 by esteemed aviation historian (and Boeing employee) Peter M. Bowers. According to his narrative, this B-29 was completed with manned turrets against the potential failure of the GE fire control system.