Lower bumpstop travel

72 dart running 6cyl torsion bars with 318.. i have the ride height set at 1-3/4 between the lca and the fram. My rock auto bumpstop is 1-3/8. Leaving me 3/8” of travel.. i may have set the ride height low but i like it where it is. Question.. how much should i cut the rubber bumper ? Or how much space does most everyone run between top of rubber bumper to frame..set for grandma driving to church specs..
thanks

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