Zero offset on 14 x 7" rim wheels for P245 60 R14 on stock 1969 Dart, anyone could tell???

Here she is before I got started. The 205 70 R14 on steel rims. I lowered the front about 1" and plan on rearching the rear of the leaf springs to lift the rear bumper about 4 inches (looks way too low now). Anyone knows how much i'll have to lift the rear end of the leaf spring to raise the rear bumper 4 inches? I read that if you use longer shackles 1/3 of the extra length will be the raised value on the rear axle so I plan on lifting 3 inches at the rear end of the leaf springs, is that too much? Will not touch the front half of the leaf spring.

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