I do not have the measurements. I would have to check that at home. What I can remember is this: I got a single piece of acrylic cut at ~10" wide and was about ~30" long. I bent it using a heat gun such that I have 2 weirs. The first weir is about 3-4" deep and long, then comes over to the rim of the tank. Then it goes down and makes another weir outside of the tank that is longer than the internal weir. I glued on sides acrylic to make the sides and make it waterproof.
I have 2 bulkheads in the external weir. One is a Stockman mod and the other is a pipe that is higher than the intake of the Stockman mod. This enables that if the Stockman intake gets clogged, I have a backup. I would have to take pics at home but this illustration should make things clear.
Keep in mind that the Stockman mod is higher in real life and this does not show the second bulkhead.
Concerning 'inviting disaster', I believe that if one takes care in designing the overflow that it is safe to use. Some people have used them for years without problems, but some have used them for one day and discovered floods around the tank. I took precautions against overflows by the beakrer inside the sump and added a second bulkhead to the weir.
Cheers, Shawn