IMO, I would not get headaches trying for KCBS; their pattern is north/south at night, isn't it?
Also, like DE said, you'll get many Latin American stations (and believe me, not only on 740), so many that you may not need Rosetta Stone after a while....
I'd say that your best bet for California would either be KNX (and I think there is a Cuban on 1070 but never got ID) or an X-bander....the 1990s were the last time I heard CA on AM, and that was about three in the X-band, before the TIS's & other X-banders sprung up like weeds.
As far as FM, one bit of good news is that WKWF 91.5 in Marathon is the only FM in all the Keys using HD. And I've heard them during times when HD is missing.
Oh...and I have tried for KVNS 1700 in the day from Big Coppitt Key, and just could not get it, despite decent equipment. KCTA, I don't think so either.
You *can* try for Mexico in the day. Cancun has R Formula 740, & XEYI on 580 (I forget the slogan). It was not long ago you could **easily** hear XEQOO 1050 Cancun in the day in Key West, even on car radio, with 35 kW in the day. I think it was Hurricane Wilma that knocked them either off air for good, or on flea power. I used to get Radio Caribe 860 Cancun and Radio Sensacion 630 near Cancun, from Flamingo in Everglades National Park. But Cubans on those 2 frequencies pretty much killed that. (I think Formula was my most recent Mexican in the day, but maybe 10 years back?)
Until about 3-5 years ago, even Jamaica was possible in the day on AM from Flamingo (and the Keys would be even closer), but there are no longer any AM stations there.
cd