Then I found a font I liked and printed it checking the size on the bit of wood.
My first brain wave re. tracing the letters was to make a print by damping the back of the paper so the ink would transfer to the wood. I reversed the lettering on the computer and placed it face down on the wood.
It worked really well, painting over it would have been easy, except for 2 things I hadn't thought through! 1) when it was painted it wouldn't transfer the ink anymore as not porous and 2) the lettering paint I used was quite thin so it needed a few coats, over the black ink might have been even worse.
Here you can see the painted version, not sure if I preferred it before au natural but at least it should be more weatherproof as it was a wood stain I used on the garden shed. I had to cut out the letters, bit fiddly. I didn't do them individually as wanted to keep them in a straight line when drawing around them so just did the tops and bottoms of the letters!
After I was able to fill in some of the missing lines free hand as they were easy but I cut out some of fancier letters individually to finish off my outline.
Here's finished outline before paint.