Might want to consider the possibility of drilling holes, cutting up some aluminum angles to remove the "angles", bending the thin metal strips into shape, then using fasteners to hold the casting together.
If the epoxy/cyanoacrylate a.k.a. Permatex/JBWeld etcetera fails, it'll likely happen as you hit a crater on the highway at 70MPH. That's when it'll be under the most stress. Had some poorly/cheaply engineered/manufactured aftermarket turn-sig mirrors on my sport bike and one ended up dangling from its wire entering an S-curve construction zone. Fortunately it wasn't my throttle side so was able to one-hand grab it and set it inside the cowling until I could get through the construction zone and off a highway exit.
Stock 2008 Yamaha YZF-R6S Blue >60k miles