These look very much like the ones I have on my masts, but mine are cast
aluminum for better rigidity and less chance of bending causing fatigue cracks at the bends. However, if well mounted with monel or stainless rivets - and - you are not excessively weight challenged - these are a fantastic deal.
As to spacing, I suggest standing in front of a step ladder and raising a leg as high as possible but not too much to be uncomfortable and then measure the distance from the bottom of your foot on the ground to the one on the ladder.