Proposed behavior:

• Add a right click UI which allows to add 4 upgrades to Armory Cabinet and allow to add them externally by right clicking with them (just like in drawers),
• Instead of displaying the item in it (like in drawers) display a percentage bar of used capacity,
• Also in the UI show the amount used over amount left (like in drawers),
• Show the upgrades and possibly amount used over amount left in the block (like in drawers)

I checked if there is/was an issue concerning this and I haven't found any.
I wanted to just upgrade the Cabinet to hold more items but it is not currently possible, so I thought of some more improvements. Also if you ever decide to implement upgrades for it I would recommend to nerf the base storage of the cabinet to 2048.
Btw I love the mod