I see reference in Galens white book as well as a Holley manual that list numbers 6404, 6405 and 6406 are for 1972 Chrysler/Mopar 440-6. Were these actually made for the 1972 model year production and then discontinued when the 440-6 pack was removed from the engine line up by Chrysler? Or, where these made as aftermarket carbs? Do they have any significant value versus other Mopar 6 pack carbs? Thanks in advance! Joe