I would look at dropping the body, battery, and switch as pointless weight, and power a single mode head from the drone battery through a voltage convertor instead, or use a 12v driver/LED to match your drone batteries. Or if you already have a usable 5v supply on your drone you could run a 3v LED through a buck driver.
This is what i advised a friend do on his.
Obv you’d need to waterproof it, i can’t remember what my friend used but he built his own drones and coated the electronics with some silicone or resin type stuff. And if you’re feeling adventurous you may be able to incorporate a remote control relay in the circuit to switch it on and off.
If you go this route though you’re probably going to need a fixed current driver rather than a FET-based one.
Personally i think the torch you linked too is going to be too floody for your purpose unless you’re always going to be close to the ground, if not you either want a bigger head or a smaller LED in the head size you linked to. If you want to stick to simply adding a full torch to the drone then have a look at the Wildtrail BLF D80v2 with an SST40 which is a great searchlight with excellent heat-dissipating capabilites, or there’s an XP-L HI version for a more focused beam with a bit more range that you might find more suitable. It’s 80g heavier and more expensive than the torch you linked to though but i think it will be a far more suitable beam than anything smaller and lighter.