I think this maybe a large it has 6 pouches on the front.
If it has 3 large pouches low down and then 3 smaller pouches with a single popper closure higher up then it's a large Alice.
You have to use the frame with the large.... So you'd need shoulder straps and a waist / kidney pad for the frame.
Alice packs are funny old things you either like em or you don't. I had a large and my view was its not the most comfy pack when loaded up. On me the frame is short so no waist belt that I fitted would actually act to take weight off of my shoulders. The pack is designed to be worn with webbing etc. But it was simple, tough and low cost.
I have a medium currently and with a light day sack type loads it's fine to use.
There is a heap of info all over the web on Alice pack modifications and heaps of after market sellers selling upgraded shoulder straps waist pads etc...
An old 20 quid karrimor Jaguar off of the bay is probably a better load carrier In terms of comfort TBH.
HTH
john