I agree with everything gerrcoin wrote and would add my experiences...
- all interior except the pilot's seat is removed from the aircraft (I
do mean EVERYTHING!).
- the right control yoke is removed
- an inclined plywood backrest is installed for the jumper by the door
to lean facing backwards against. This allows the jumpmaster to kneel
and bend forward over this jumper, effectively placing two people where
the right seat was, or three people above and slightly forward of the
main gear.
- this leaves room for three more jumpers (on a cold day) in the rear.
Four jumpers and the pilot are a normal load.