In your second picture, the band adjusting lock nut and screw are backed off. My guess is it was out of adjustment and the piston came out too far blowing the retainer past the snap ring.
RCI fuel cell, single out, single vent. Foam filled 16 gallon w/ straps. Been sitting for years. 0-90 ohm sending unit. $100 plus shipping from 12534.
Disregard throttle body pic, sorry.
Price reduced on fuel cell....$80 plus shipping.