Photos of 41 Cdo around the time of the Chosin Reservoir battles show them fully equipped as per the USMC, ie with US helmet as well. Since this was mid-winter, they are rarely pictured with steel helmets, rather they are swathed in whatever protective clothing they could scrounge. Many photos purporting to be 41 Cdo show them with a mix of UK & US kit and weaponry - e.g. Garands and Lee Enfield No4s in the same picture. It is likely that they were re-equipped after Chosin with standard UK stuff, but that they continued to retain the favoured bits of US equipment.