There was a model that had the old style flat spring and a long tang that was changed to the coil spring and a short tang like the 336 still has. It was either the Model 1936 or Model 36. I did a post about the changes not too long ago but I'll be darned if I can find it.
Oops, I found it. It was in a private message about blued receivers on a Model 1936. It was this model that the change over was made. So therefore a stock from a 336 should be a close fit on a Model 36.