I would like to fine tune the mechanical advance on my truck, 85 360 in a W350 crew cab. I'm thinking "All In" around 3000 RPM. Currently it seems to be about 4000 RPM. What spring/springs would get me in the ball park? I know this could be some trial and error. Stock distributor, Would just the one light spring get me close? Or some other combination???? Thanks for any ideas.

67 Charger 383 auto
75 Dodge CNT 800 CAT Diesel
2012 Ram Crew cab 5.7 4x4