The casting department for next season's Dynasty spinoff, The Colbys, is tossing around some big names. Charlton Heston has signed to play the family patriarch, and Maxwell (Grease 2) Caulfield will play his son, Max. Faye Dunaway and Elizabeth Ashley are leading contenders for the role of Sable, Heston's bitchy wife on the show. Word is that Angie Dickinson is up for the part of Sable's sister, who's also the mother of Jeff Colby (played by John James). Contrary to rumor Elizabeth Taylor will not be joining the cast.... [P] Billy Joel's former wife and manager, Elizabeth Weber, won't be outsplashed by her ex's nautical nuptials to Christie Brinkley. Later this month Weber will wed video producer Steve Sterling, whose credits include Grace Jones's Honda commercial, at a resort in Sandy Bay, Jamaica. Invited guests have received a Wall Street Journal style newsletter, titled the Wedding Journal, advising them to bring plenty of sunscreen and to avoid making drug deals while in Jamaica. [P] Michael J. Fox, who makes his big screen debut this summer in Back to the Future, has found that Family Ties are hard to sever. Fox had to turn down a lead role in John [Breakfast Club) Hughes' upcoming movie Pretty in Pink because NBC wouldn't give time off from the sitcom. [P] Director William (Cruising) Friedkin's new movie, To Live and Die in L.A., about two U.S. Treasury Dept. agents who try to nail a counterfeiter, has itself become the subject of a federal investigation. It seems Friedkin had more than $1 million in fake $20 bills printed up, which were supposed to be burned as part of the film's climax. But in May counterfeit twenties began circulating in L.A., and Secret Service agents from the Treasury Dept. traced them back to the movie set. The serial numbers on the fake bills matched those on the printing plates used by Friedkin. According to Al Joaquin of the L.A. field office of the Secret Service, about $500 in bogus bills—which Friedkin claims bear the words "not legal tender"—have been recovered. Though the feds are not disclosing the results of their investigation, one member of the crew has been feeling the heat—novelist Gerald Petievich, who wrote the book on which the screenplay is based and who co-authored the screenplay with Friedkin. Petievich is a badge-carrying Secret Service agent, who has been put on paid suspension while the investigation is under way. Fearing that Petievich's story is too realistic, the Treasury Dept. recently demanded to screen the film, which is to be released in October. Friedkin has put the film under lock and key, saying, "Tell them to get a subpoena. This whole thing smacks of McCarthyism." [P] Down Ft. Lauderdale way Peter Falk is filming Happy New Year, in which he plays a jewel thief. He reports that he has selflessly put himself at risk to film a bedroom scene with his co-star, Wendy Hughes. "I've heard that more people die in bed than anywhere else," says Falk, "but I'm willing to take my chances." [P]