Divecon,if I understand what you're asking, if you cut the 33's down to 29", they will shoot much stiffer. Also, the reason we offered three lengths was to allow archers with different draw lengths to select the one closest to their draw, to keep the barreling as intact as possible. It complicated our production considerably, and I would do it differently now, and only offer one or two lengths. And yes, the higher spined shafts are heavier in weight. For modern longbows and recurves, for a 70# draw you will need something in the 95-110# range, depending on setup.
Jeremy, thanks for that conversion. Remember, this chart is almost twenty years old, and AMO was the standard. It's not exactly AMO, but it's close, and based on our actual test results.
Fred, Shaun is right on. If you don't bare shaft tune, shooting your broadheads will tell you if the spine is right. With field points you can be one or two spine classes off and the feathers will correct the flight so you don't notice it, but the broadheads will tell the tale. If you want to do some testing, I'll hold off on preparing the 70-75's you ordered. I feel sure the 75-80's would work too, especially with some front loading.
I know what you mean about breaking shafts while testing- it works best for me with a very soft target. I use a big soft cube of furniture foam, like the cushions of a sofa are made from. It absorbs the energy of the arrows without breaking them.