Opinions vary. Few tight chokes shoot slugs well. With the exception of the Polychoke little damage results using the Forster style projectiles we call "Rifled" slugs. The hollow base design swages down OK in tight chokes but accuracy oft suffers.
I'd still go easy on shotguns that old, and chances are that 12 has 40 POC, darn near a turkey choke wioth modern ammo.
I'd keep your classics for use with shot and spend a couple hundred on a new or used Big Four pump with sights. One of the 870 Express variants has a 20" slug barrel with choke tube capability, this would make a fine addition to your battery.
HTH....