Hiya Stray,
If you know of anyone with a 3d printer, you could try and make a sample widget for playing with size/shape. Print it, then modify the design with any changes, print...test...rinse repeat.
I find its an easy way to fine tune any weird one off thingammys. As an added bonus, the 3d software will keep all the sizes and angles so you have a thing to take angles and measurements from even if you end up making one out of wood or steel as the finished product..(and its all freeware).
This is a quick go at a 3d model of it, this took about 30 min (sorry its a bit rough on the scale and measurement), so it's not hard to make a basic model. And I'm a numpty at this stuff, so you don't need much skill.