So I'm midway through making the trebuchet it occurs to me: how the hell does this thing work!? I have now spent a solid number of hours rewatching clips from Ironclad, Kingdom of Heaven and the Battle of Minas Tirith featuring trebuchets so I can get them at different angles and see the areas I couldn't see before. In addition to this all siege weapons in gneral appear to be designed differently which really didn't help, however for the trebuchet I decided to merge the ones I saw at Caerphilly with the ones featured in Return of the King, since I was able to find the most reference on this model.
The greatest challenge was learning how the release and winding mechanisms, because the player would be able to get right up close the the engines I had to make sure the winches and mechanisms were all correct and appear that they would operate correctly, even though I had no intention of making them interactive elements. The majority of my search results were toy models, home-made DIY replicas and remade models; don't get me wrong they were helpful in terms of design, however many of them were rather basic and lacked all the required mechanics.
How do you release that!?
This is an example which covers many of my results, it's got the wind up mechanism but there is no way for it to be released!
Eventually after refining my search I was able to find a page committed to Trebuchet Triggers, it was as if someone knew precisely what I was looking for and presented it to me! Several of them were appropriately named mystery triggers were there is no visible mechanisms in the provided images, however I saw this trigger which seemed to make perfect sense.
With this new insight I'll update the model and get the mechanisms in order.