Bismuth shot is used as a non-toxic alternative for older guns that would be damaged by steel shot. Not necessary unless you are hunting migratory birds (waterfowl) or are turkey hunting in an area restricted to non-toxic shot such as a Federal waterfowl production area.

Your concern is valid, there are many 2.75" lead loads around today that have power levels never dreamed of in 1940 in a 12 gauge. Mostly this is due to advances in powder burn rates, so that the pressure levels are still safe despite pushing larger payloads much faster. Still, these loads push the pressure limits to the maximum levels and I am not comfortable with the idea of stressing an older gun, not to mention the increased pounding on that old stock and internals from recoil.

IMO, stay away from the 1400-1500fps loads with 1 1/4 or 1 3/8 payloads and you should be fine. The old standard 3 3/4 dram eq. load of 1 1/4oz. at 1330 fps would be the maximum I would use.