Most of the stock carbs on the 401s are Carter Carburetors, the same as what is now Edelbrock, Edlebrock bought Carter.
If you look at the list of links at the top of this page, the first one will take you to CFM recommendations. For a 401 the recommendation would be 579cfm to rev to 5000rpm, so a 625 cfm would be adequate.
95% of carburetor problems are solved in the distributor.
Nothing beats an original for fit & functunality that's been properly set-up for your vehicle by the OEM manufacturer. By the time you mess with, tune & buy all the nec. parts to make the replacement compatable you will have spent almost more than what it costs to rebuild.