does anyone know what the stamped number M 098504 MEAN ON THE FRONT FACE OF THE RT CYLINDER HEAD

 

That's the engine unit number. The "M" means that those heads were originally installed on a 2bbl 425. The rest is just the engine serial number. If your have the Protect-O-Plate for that car, the engine unit number will be on the P-O-P along with the VIN.