According to http://www.designation-systems.net

Letter (1) = Category of equipment… L = Accessory or attachment

Letter (2) = Purpose of equipment…. A = Recon

And they say that an LA 51 is the Lens Cone , not the camera itself.

There should be another ID plate on the camera body which probably will start with KA….. so it might be (say) a KA 51 camera or similar.

Hope that is of some help