Glenn,
Your idea to make a lure that's the same size. falls at the same rate and has the same action as the original, but is lighter, is a tough nut to crack, especially on a walking glider.
The walking action relies on uneven distribution of the weight, with the back half of the lure heavier than the front, so it has more inertia in the water. The lighter front half of the lure yields to the resistance of the water first, so it turns as the heavier back keeps going. Kind of like a jackknifed trailer.
Overall weight is what makes the bait sink at the same rate.
And shape is what affects hydrodynamics, which is how water passes over the lure as it is worked.
I'm afraid anything you do to lighten the lure will affect one or all of these characteristics.
Myself, I'd probably settle for a smaller version first, so I could retain the same basic design but make it lighter by virtue of it's overall size.
But I feel for you.
Good luck.