First off there is NO VIN on the rear axle assembly on any mopar of that era .

68 is stamped on the bellhousing flange near the oil pressure sensor and in the same spot on an automatic or on the id pad on the side of the trans on a 4 speed . It will be the last 8 of the VIN , and will NOT match the number stamped on the body . the only way to tie the body number to the VIN is with the FACTORY BROADCAST sheet .