Rory, the lyrics have surfaced: https://mudcat.org/thread.cfm?threadid=167730#4051732

I was uncertain of two lines which were subsequently aided by Phillip.

In case you also missed my message on that thread, I've linked it here and I'll also re-iterate my opinion that the best place to get info about the song is from the singer himself: http://www.rorymcleod.com/

I haven't tried to contact Rory, but since you seem rather passionate about this song and songs of the Spanish Civil War in general, I think you'd be in a much better position to learn from him than I.