I second using a pin and epoxy - drill the holes for the pin a bit oversize (unless you have access to some pretty fancy equipment you'll never get the holes perfectly aligned). Dry fit with the pin - if necessary open up the hole enough that you can get perfect alignment with the pin in place. I'd recommend "JB Weld" epoxy - after mixing, fill the pin holes before installing the pin then assemble and support so it'll stay aligned until cured (JB Weld is super strong but it's slow cure - I'd give it overnight).
You probably want to figure out how you'll hold it in alignment before you add the epoxy
