Many thanks arthurk. I'm still very keen to figure it out.
I am fairly settled on the bottom three lines being -
do not let this / be broken / your father
The part I'm struggling with is the first two lines:
Top line, I think the top right word is "Gibson". What might the top left flourish be? One letter or two? An "H" or an "S" maybe, or an "Fl"?
Second line, I can see so much of it, I'm surprised I can't figure it out. There is a middle "sp" which might be an old "ss".
(Obviously the following mark-ups assume that I'm seeing the right letters)