Frank, there is no way the grade difference between the inner and outer loops of your helix is as large as you calculated. The run on the inner loop is much more than 16.75', I'm not sure how you arrived at that.
Outer loop, 8" rise in 3.5 turns @ 22" radius: 8/(3.5*2*pi*22) = 0.0165 = 1.65%
Inner loop, 8" rise in 3.5 turns @ 18.25" radius: 8/(3.5*2*pi*18.25) = 0.0199 = 1.99%
You should be fine. As a sanity check, with an 8" rise in 3.5 turns, you should have about 2.25" between turns. Is that what you have?
-gfh