I have been threatening to make this for the last few years. I made the frame out of some old Douglas Fir. The print was enlarged for me by a photographer I met in Kyushu Japan in January. He has a nice studio and some quality equipment. After messing up 4 mats, I finally got one that looks a little like the pros. I used a Logan push cutter, ( the cut over-lap is very important) the back edge of the cutter base should sit on a line 5cm away from where you want the cut. If the cut doesn't overlap it's near impossible to hand-cut into the corner and there's no way you can recut it using the Logan.
I mounted the print slightly higher than centre, but in hindsight would raise it even a little more next time. I have an interesting print for the next one I'll do and with my teach yourself photoshop interest, I'm looking forward to it.