Haven't had much time to work on the oak sled for the GB mortar, every time I get a free afternoon it rains.
So I've been tinkering with the Marsilly carriage in CAD. Thanks for the link GGaskill, but I think I have it worked out to my satisfaction. It was never meant to be a nut & bolt reproduction. What I wanted was to build it to fit the barrel and hardware that I have, while keeping the outward appearance of the design.
As far as construction, the main prerequisites were that it use these old iron wheels:
..and this brass elevator screw:
I made this elevator when I made the one that I used in my field carriage. The two antique brass faucet handles were bought from the same source:
This is what I have so far: