Take a look at AC105.2C........lot's of good info there & lists a bunch of the STC's USPA owns. Also;
US Parachute Association, 1440 Duke Street Alexandria VA 22314 United States
SA1-188SA1-188 Removal of right door, right front seat, right control column, and right rear window (optional) and Reissued 1995101810/18/1995
SA1-193SA1-193 Conversion of aircraft for parachute jumping operations. Reissued 1995101810/18/1995
SA217WESA217WE Removal of cabin door to permit aircraft to engage in special operations such as aerial photography, Reissued 1995101810/18/1995
SA4-1593SA4-1593 Removal of door for parachute jumping and aerial photography operations. Reissued 1995101810/18/1995
SA40CESA40CE Removal of left or right door for any purpose. Optical removal of right front seat, with occupant
US Parachute Association, P.O. Box 409 Monterey CA 93940 United States
SA367CESA367CE Removal of right front seat, rear seat, and baggage shelf (if installed). Installation of floor Reissued 1972102410/24/1972
SA874CESA874CE Removal of right front seat, rear seat, and baggage shelf (if in- stalled); installation of floor