Icelandic goat hair dress sporran in an Edwardian styling.

[Theowulf]

I can only echo, beautiful work!

A drawing would be great if you're up for it. Your description is clear and detailed, but I'm becoming a visual learner as I get older :-)

[Shinenotburn]

Here is a quick detail of how I did this cantle. Hope this helps. These old silver plated frames often have wood backers on them that can be reshaped or cut as needed.

One other thought... On the sporran itself, I hollowed out a little pocket in the backer panel of the sporran that allows for more room in the flap pocket.
The backer panel is made from heavy leather sewn and glued onto a thinner more softer front piece that the hide is then glued and sewn to. This provides the backing for the flap pocket interior and gives one more room inside.

Hope that all makes sense to everyone.