[Retlaw]

That structure must have had a purpose and I'm open to suggestions (other than being horse-drawn) as to what.[/quote]
From my last post. The structure had a purpose.
It is shown by the eye on the rear of the cannon & the eye at the front end of the carriage, they are for attaching the ropes & pulleys for return to battery position, after firing and reloading.
You mentioned steering, that implies transportation too another location. I don't intend to be negative, just can't see the point of making a replica, why not make a 1/8th scale model of a complete cannon & carriage and put it on display some where safer than up the Coppice.