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An overdrive with a 3.54 rear axle ratio can be a strain on the engine if used in high range in hilly country driving. I am a long time Model A owner, not a mechanic, but an engine overhaul should be good for around 80,000 miles with one check on the bearings somewhere in the middle of those miles. If you hear suspicious knocks at any time check right away but the norm is for a longer time span.