The 412 was not mfg with steel shot in mind. Having said that, the barrels are tough modern steel and quite meaty. So I would concur, anything up to a mod choke should be OK. Imp mod with smaller steel shot only ie no 4 and smaller. Full choke no steel at all. The chokes are marked on the side of the breech.

The later 512 was offered with 3" chambers and screw chokes and could be ordered with special "steel shot proof". Some were made with 3 1/2" chambers.

It's not an "old" gun at all, in the scheme of things.

But if you just want a shotgun (not a system gun), then there are lots of choices. The 412 and 512 are rather heavy as shotguns. About 8lbs!