Here is a link to drawings of a Hesse-Casel I pounder from the Marburg Archives (no 28.0) - the other drawings on this site are also very useful: http://www.digam.net/document.php?dok=6465

I don't have plans for the Hanoverian pieces, but would expect them to be similar (same calibre and also used to support light troops) - from memory, I don't think Scharnhorst discusses them in detail, although he notes their use by the Hanoverians in Flanders and earlier