Well, the problem you've got with the parabolic curves is that the radius is constantly changing, as it velocity.
radial(?) accel is basically velocity/radius of the curve.
Remember to add 1G at the bottom of a drop.
Negs are the same, but remember to add a G. [your accel should be negative until adding the G. Most coasters 'negative Gs' are actually between 0 and 1G. Magnum might actually go negative in a couple of seats. [1.3 comes to mind]