Book cover as gift

I would like to have a book cover image produced that I can print for my father's 60th birthday. As children (about 25 years ago) he invented silly stories for my brothers and I about two hapless British policemen called Constable Fiddly-Diddly and Constable Wibbly-Wobbly. It would be great to see them come to life as illustrations. Ideally the image would include both characters, some basic background and the lettering for the title/author.

I have attached some files to give an idea of style etc but happy to discuss.

Thanks.