The actual Chrysler 300 J for 1963 is a rare car. I can not tell with the information given and the pictures supplied if this is an actual letter car or not, my first impression is that it is probably not. Closer inspection and a vin number verification would be needed. The cross ram setup could be ordered on other models besides the letter series if the dealer knew what he was doing. The fact that the seller is unwilling to part with the air cleaners is big turn off for me. The car is might be a non letter 300 series with the 390 horse engine. These cars are worth a lot less than the letter series. If the car can be verified as a letter series car, it is probably worth close to the asking price WITH THE AIR CLEANERS!
Dave