The Old West died hard in the City of Angels. And in the years after World War II, battle-hardened veterans came home to a town “under enemy occupation,” when the only way to fight off the Mob was with a six gun, your two fists and the right hat.

“Gangster Squad” is a gang-war drama built on Western conventions, a rootin’ tootin’, Camel-smokin’, whiskey swillin’ shoot-’em-up about a lawless period in L.A.’s history, when a small cadre of cops working outside the law, took on Mob boss Mickey Cohen in a fight for “the soul of Los Angeles.”

Josh Brolin ably handles the John Wayne role, the paragon of virtue, an incorruptible police sergeant tasked by the only honest police chief (Nick Nolte) to chase out mob boss Mickey Cohen (Sean Penn, pugnacious, ferocious).

Ryan Gosling is Jerry Waters, the cynical detective/gunslinger who will have to take sides, but is going to take some convincing.

Anthony Mackie’s the knife-throwing street cop from the black side of town. Robert Patrick is the aged pistolero and holdover from the “real Wild West.”

Michael Pena represents the city’s Hispanic underclass, a kid who needs to prove himself. And Giovanni Ribisi is “the brains,” the cop with the glasses and the Army-based knowledge of wiretaps. They’re a regular “Magnificent Six.”

“Who’s the tomato?”

That would be Emma Stone, playing the “dance-hall girl,” the mobster’s young moll “poached” by the handsome Jerry.

“Zombieland” director Ruben Fleischer may not do much with this pictorially that suggests “Western,” but he keeps the characters iconic, the morality straightforward and the action clean. Will Beall’s script is peppered with character “types”: gunsels with scars and World War II-vintage machine guns. Of course Jon Polito shows up, as he has in every gangster period piece since “Miller’s Crossing.” And Beall’s dialogue gives “Gangster Squad” an extra kick.

Insults: “He’s got a smart mouth, but he’s dumb where it counts.”

Compliments: “Push comes to shove, kid’ll stay behind his gun.”

This “inspired by a true story” tale has much in common with an earlier Nolte fedoras-and-fistfights cop picture, “Mulholland Falls,” named for a hillside where brutal cops sent gangsters tumbling after one of their “Get outta town” lectures. Brolin & Co. even pay a visit there.

All in all, “Gangster Squad” is a solid piece of work, and that solid piece of work Brolin anchors it in the kind of square-jawed moral rectitude that makes you wish Hollywood made more real Westerns, just for him. He’s fine in a trenchcoat and fedora. But somebody get that man a horse.