need ride height specs for 74 duster

What are your actual alignment specs?

Positive camber should only be used for bias ply's. Radial tires should be set up with negative camber, as the chart above shows. The factory specs were for bias ply's, and are WRONG for any kind of modern radial tire.

But if you're wearing out tires that fast I bet its more than just camber. Camber has to be pretty extreme to cause rapid tire wear. I've run as much as -1* on the street with no abnormal wear whatsoever. If your tire wear is that bad, I would suspect your toe settings first.

-.5º camber, +3º caster, and 1/16" to 1/8" toe in is a good place to start.