I couldn’t find the tail panel in any brochures or old photos. After more research it looks like the letters on the tail panel are from a 68 Coronet grill.

The VIN is WM21N0G which appears to indicate the car is a Coronet/Medium (trim class), 2 door sedan, 383 hi. Perf., 1970, assembled in St. Louis. That would indicate it was possibly a Superbee. It also seems like this supports that. 1970 Coronet info