I have seen a reference to this combination, with a photo, but can't find . I did find this, which has a line drawing from Singer. It is shown with a bentwood cover, but a 3/4 size coffin top portable likely has the same dinensions.
http://needlebar.org/main/singercabs...t10/index.html
Hand cranks were more widely available/used than treadles in the UK and Europe, due to home/space limitations. (Ibelieve I read) When the family moved up in station, they would upgrade that portable hand crank by adding the treadle.