Similar to how Tallyho does it but with more customization, instead of a block which when interacted displays the Scope next to the cannon and Thermals some blocks above the player, make it need to place optical, which can be linked to the display, and then interacted to have the view of them
Scopes - Simple scopes that can be zoomed in and out, maybe have it possible to add the marks of shell drop or follow the cannon pitch
Night Vision - Have it apply a green filter on your vision making the dark brighter but have it basically blind you at day
Thermals - Have them apply a white or light gray filter and a grainy effect to lower a lot visibility, but make entities bright
Cameras - Let them have full axis control of Pitch and Yaw for a good view, if placed on top of a block have them move in a 360º circle, while when placed on a wall limit it to 180º