Leaf Spring Suggestion for 70 duster
In my experience, Laura at ESPO spring&things is a GENIUS - easily the most knowledgable vendor I've ever dealt with.
I went with their 2" over height springs in my 73 Duster. I know that's not what you are looking for - just a plug for a great vendor. She knows everything about everything she sells.
I also put a 1.25" Hotchkiss front sway bar in my car and it made a HUGE difference. I don't autocross, but cruise around town.
Hope this is helpful