leaf spring location after moving inboard

i dont have the leaf springs yet, sense the leaf springs are directly under the rails if i measured from outside rail to outside rail would i be aboul to use that number to place them?

Measure from the center of perches and move 3 inches in.Thats how I did mine.I left the old ones on and used a straight level for pinion angle then tacked the new ones in place,removed old ones,then welded new ones.Worked for me.:D