Thinking about replacing my leaf springs, and I need your advice.

Rick - thanks for the offer. The 79 HP dyno run was on my previous Duster that I no longer own. I had a speed shop performance tune my current Duster and it runs a lot better, so I'm happy with it. But I'll keep an eye on the slant six area. Thank you for the recommendation!
Glad you're happy with it! Think you'll be amazed at the wisdom found in that /6 area. No kidding, those guys can often make things happen that other professional shops have no clue about!