As I am fortunate to have access to a laser cutter, I laser cut the fiddlier parts of K-9's head, the rest hand cutting it using my trust Olfa knife.
I had also purchased a piece of 20x20x1.5mm aluminium u-channel (purchased from Bunnings) that day, so cut that into the 233mm and 340mm lengths. A drill press helped make sure the holes were aligned front and back. Using a smaller guide drill bit initially, also made sure there was less clean up in the holes. Getting the right sized counter-sunk screws were a pain, and had to go for imperial sided ones (purchased from Mitre-10), but they seem fine. I used four, using a couple washers at the back, and super gluing the bolts tight. Everything was sanded clean and smooth, including the tops of the counter-sunk screws.
Just a little note, I used the Antenna Support pieces as a guide for the location of the screw holes on the actual U-channel, to make sure when it comes to bolting up the neck to the support that all the holes will line up true. Below is the completed Aluminium Neck Assembly.