I am making some rear shackles for my 95 pickup and I was looking at the downey set to compare. They have 2.5" of lift but it that 2.5" longer than stock or 2.5" of lift at the center of the axel? I calculated about 5" longer than stock to achieve 2.5 at the axel, is that right? 8" center to center shackles seem a bit long?

 

your calculations are correct. Any increase in shackle length will result in 1/2 the lift-- 1:2 ratio. Not sure about the 8" C to C, but that does seem a little long...