The metal monitor mount has tabs formed into slits to restrict its movement back and forward. To be mounted the tabs have to be bent out of the road. To do this I used a set of pliers to lever them out of the way- shown in the second picture. When the tabs have been bent out of the way the mount can be straitened out.
I then measured the 60 mm (the width of the wood) from the pivot point and made a mark with a marker. I then drew a cut line using a square for accuracy and clamped it in the vice to be cut. Note in the picture I have made sure the line to be cut is as close to the vice jaw as possible to reduce vibration when cutting.
I used a hacksaw to cut the excess material off but if you have an angle grinder this will be much quicker. Once cut it is a good idea to use a file and remove any sharp edges left after cutting.
To allow mounting of the brackets to the wooden frame with the M8 bolts an 8 mm hole must be drilled. On the brackets here there was already a hole that could be widened. If there is not you will have to measure and mark the centre before using a smaller drill to make a pilot hole. Once you have a pilot hole you can then drill it out to 8 mm. I have a small press drill but a hand drill would to the job fine.