blueprint from the adjustable front spring hangers used on the australian Valiant charger RT suggest the holes should match the bolt you use for your 6 or v8 sized bushes.
3 parts need printing matching together and sticking..
might be a starting point
but keep in mind adjsuting the height of 1 end of the spring has an impact on under/over steer
which si why these had two holes one for twisty short track use and one for 24 hour race long road track use. the effectiveness potentially greater on the aussie car 8 inches shorter and 2-3 wider at the back
Dave