Annydrite

Hi, I am new to astro photography and am building a barn door tracker. I was thinking of building a type 3 tracker. I also see where a type 4 can achieve much longer tracking. While I do not need tracking to last that long I have a question regarding construction. I see plenty of pictures that show the construction of a type 3 drive with 2 inch hinge spacing and a beta of 2. As far as I can tell type 4 is a beta of 2 and the layout of the boards is the same. Is this true? The classic picture from Dave Trotts article shows them from the side view and dose not really make sense to me. It seems type 3 and 4 are the same as the sliding point and drive arm are the same. The 3d drawing seems to show a type 3 with a bata of 6.