Since "overdrive" indicates that the driveshaft is turning faster than the engine, 2100 engine RPM in 5th. gear against a 2.73 rear axle would probably be somewhere in excess of 90 MPH with a normal size tire. Are you sure that axle ratio isn't actually 3.73? I don't think I've ever seen a stovebolt six that would be able to pull a 2.73 gear behind an OD transmission.
Jerry

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