It's a 1981 model 610.

Carbon manganese alloys such as Mangalight were slightly weaker than CrMo but much easier to braze and suitable for mass production. Consequently they bridged the gap between hi-tensile and CrMo both in terms of strength and cost. While we don't have figures for full Mangalight tubesets, most other carbon manganese tubesets increased the wall thickness to compensate for the slightly lower strength. This typically resulted in a weight penalty of about 10% over CrMo, accompanied by a slight increase in stiffness and a corresponding slight loss of resiliency and shock absorption, though most owners cannot detect the difference. The total weight penalty on a carbon manganese fork would end up being well under 10% once you factored in the weight of common components such as steerer, crown and dropouts.