Hi, not sure what the 4 actually means, but it was only ever given to the E49 chargers. These were the fastest of the lot. Of course it's likely that this one is just a replica as E49s are worth ultra-mega-megabucks nowadays.
From Wikipedia:
"In 1972, option E49 was released for the Charger R/T, whereby a more powerful (quoted at 302 bhp) version of an E38-style engine was mated to a four speed manual gearbox. This engine produced remarkable torque on a seven bearing configuration which enabled considerable power development previously unobtained from 6-cylinder engines and not surpassed until the Porsche Turbo 911 (300) release of 1975"