I have had very good success with CPP in the past. Stuff happens. If your new and old drums don't fit their hubs, send them back. Maybe they will take the time to figure out what went wrong with your order (wrong part in the wrong box probably). They don't want to sell bad parts any more than you want to buy them. Its bad for business. Its difficult for them to figure out what is off over the phone.
Also you can bet money that they get all kinds of calls from folks who have no business trying to work on anything mechanical, and have to take the time to try to walk them through doing something which they have no business attempting. (Not you, BTW.)
Carl

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission