Here is a little Trick on the Edelbrock side of the game.
1403 - 500 electric choke
1404 - 500 manual choke.
1405 - 600 manual choke
1406 - 600 electric choke
Change the 14 to 99, and you get Edelbrock remanufacturered carbs, at a much lower price.
9903 - 9904 - 9905 -9906
scummit racing has the 9905 600 cfm manual choke at 199.95 right now.