Thanks for your help Sarkut
Out of curiosity I googled the same question and found another tutorial that I did understand.
imported modern image and made a new layer, imported the monochrome, deselected the modern, 'select all' on the monochrome, 'paste' to new layer, jiggle it about a bit to line it up and 'flatten'...job done and one merged image!
Thanks for your patience though!
Best regards,
Pickard.