How to calibrate speedometer?

abodyjoe said

its easy to switch. the piece where your spedo cable screws onto has a retaining clip and pops out. when out the gear slides right in.

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I agree. Its easy. I've done a few 727's. I personally base my speed by pace and RPM. Hahaha, yes my speedometer is disconnected.
Moparts.com has an awesome archive of tire dimensions from old school to new school. Also The Mopar Six-pack book has a chart in the back of the book with gear sizes that work with your application. Digital is the most accurate.