[Retlaw]

Originally Posted by SoulManic

Here are the photos of the carriage in its current state. The first thing to note is that it is upside down.

Picture 1. The square cut-out would be for one of the axle blocks. The large scallop cut-out would be either decorative or for weight reduction and was between the two axles along the bottom. The small block hanging on its side shows the cut-out for the trunnion on that side of the cannon.

Picture 3. The end of this side which would have had a matching axle block cut-out has gone but the the large scallop cut-out is there.

Picture 4. This is probably the front block with a scallop cut-out on which the barrel would rest at its lowest elevation.

I agree that it was probably a ship's cannon and to get a better idea of what it looked like (it's difficult to see detail on the postcard picture) take this link to an 1823 French ship's cannon.
french1823

If you take another look at the picure of the cannon in Corporation Park, you will see a lkeness to your carriage bits on the Coppice.
The one advertised as a French cannon, has a different recoil eye, and the carriage is nowt like your bits, or the one in the park.
Retlaw.