Polikarpov U-2 with Bakshaeva cassettes

[Jjr]

Hi
Who can help me with drawings/pictures (which shows the construction) dimensions, used materials of the Cassettes which were used on the bottom wing of the Polikarpov U-2c and the U-2C2c, which were used totransported persons on a stretcher?
How was it constructed on the bottom wing?

Thanks
Jan