That write up is very good, I would only add that I remember seeing another one somewhere on the DSM forums which was also very good.
I mention it mainly because the author of that write up gave the sizes of two hole saw attachments for a power drill (the type used to drill circular holes for installing gauges etc). When cutting the opening in the hood he cut two holes which followed the radius of the edges at each end, then he cut a straight line on each side to remove the material left between the two holes.
At the end of the day both methods work and once the catches are installed any rough pieces should be hidden. I just thought the second method sounded much easier.