The only photos we have are posted here. We have no idea where you could get a drawing of this carriage; maybe these pics are enough to get the shape and details you may need. This is the one we recommend, but there are other good looking carriages out there.
This one can be made of low carbon steel by machining or fabrication and welding, especially in your 1/5 or 1/6 scale. So, here they are; hope they help you both out Ben and Robin.
Regards, Tracy and Mike
The shape of the cheeks clearly in view here.

Trail details here; notice the brace plate, lunette and elevation crank.

The trail cross-section in view and yours truly who was here on the Upper Parade at Norwich University for just the second time since graduating in 1969 forty years ago. We fired this gun every evening during the four years I was there.

Another carriage of the same type on the N.U. Campus; this one still has it's breech block.
