I looked and do not seem to have a picture either. They used the 10 inch 57, 58, and I think part of 59. There really is no keeper just the stud with a holding nut and the felt pad that is often missing. Anyways, when the springs are installed correctly in behind the shoes, the shoes with bend inward and can be pushed out with the little screw and felt until the shoes fit nice. At least that is how I remember it.
If you have not put the springs on in behind the shoes, place both shoes with the springs in back on the floor then grab the shoes with both hands and stretch the entire assembly at the same time over the axle lug nuts while keeping outward pressure so everything does not fall loose . You probably will need to fettle with it some to get it over axle
Does the Moss catalogue show a picture of the springs? I have seen a picture somewhere, but it has been awhile, and I will look through my books. Do you have a large original copy of the tr2 and tr3 book that should have a picture? Usually the shoes themselves are too large to fit nicely in a 10 inch drum probably because the shoes are aftermarket; you might need to fix that.
Keep us posted steve