To reach the newsroom of L.A.’s newest newspaper, you’ll need to take a walk through New York. Or at least the Fox lot’s version of it — a few blocks of make-believe old-timey Brooklyn lined with brownstone facades, rusty fire escapes and the sort of soot-stained concrete stoops that Slip Mahoney and the rest of The Bowery Boys loitered on between capers.  Almost too perfectly, this is where Rupert Murdoch’s California Post — the conservative media mogul’s attempt at a New York Post -style tabloid for a West Coast readership — has set up shop, on the fourth floor of the backlot’s Building 89, overlooking the one place in L.A. that’s pretending to be Flatbush.  “I have to admit, it feels like home,” says Brooklyn-born Ian Mohr, one of the New York Post editors who moved to L.A. to help start up the paper. “I go downstairs, and it’s like I’m in New York. Only it’s quieter.…