David, AM reception can commonly be improved by turning the radio on its axis until you get a better signal... try that with those units.
Also, the pull-out antenna is not for the AM band... that is for FM, so it doesn't need to be extended.
C. Crane has a reputation as a customer service-oriented company... give their toll-free number a call sometime and ask if they can give you some more ideas to improve AM reception. They used to sell a very specialized AM antenna for $50-60 that should pull in just about anything. It's not one of these...
C. Crane Company - AM Antennas - Toll Free (800) 522-8863 ...it looked like something from the '50's. I think they have more items in their free print catalog than they do online. Look on that link for a list of things that can cause AM signal interference.
Also, take these radios outside and see how the reception changes. In my experience, AM signals are very susceptible to being shielded when indoors... depending on how deep within a structure or how much metal is in the structure. Sometimes, just putting the radio on a window sill makes the AM reception a LOT better.