Neo-Nazis believe a mysterious potato farmer known as “Scary Larry” is the infiltrator who prosecutors say shacked up with Southern Poverty Law Center boss Heidi Beirich. Former National Alliance member Lawrence W. Myers — an Arabic-speaking, guitar-strumming, “paranoid” man — was even kicked out of the racist group for being a spy, sources said. Multiple ex-members told The Post they believe Myers, 68, is the person labelled with the pseudonym “F-9” in a recent federal indictment, who feds claim was paid $1.2 million from SPLC donor funds. Lawrence W. Myers is described as a mysterious, Arabic-speaking potato farmer who plays...