Hi, zkmark.
You can bring the Weapon2D (and its dependencies) to the Input-Aligned Movement project and add it to the Player scene.
Use a RemoteTransform2D as a child of the CharacterBody2D pointing to the Weapon2D.
You can essentially mirror the same structure from the Player scene in the Ability Loadout Switching project, but using the InputAlignedCharacterBody2D instead.
I will write down a tutorial for you this week and will come back here with the link. Stay tuned.