I don't remember throwing anything out of the back of an Argosy made of wicker. It's a long time ago but I had it in my mind that SEAC packs were canvas containers weighing about 250 lbs.
The most common delivery method up-country in Aden was the 1-ton container which rested on the roller-conveyor floor of the freight bay and were pushed out over the sill of the clamshell doors by dispatchers. We would normally deliver 8 of those.
We also had the ability to deliver two MSPs (Medium Stressed Platforms) which would typically each contain a Landrover and trailer but to my knowledge, this was never used in anger either in Aden or even later in Oman.
Interestingly enough, there were several up-country strips (Mukeiras comes to mind) where we could have happily operated into but the powers that be in MEAF HQ would not authorise us to operate to Military Operating Standards. So, by applying Performance A standards we were restricted to the extent that we could actually deliver more payload by parachute than we could by landing!