Hi, jordanr7. Do the howitzer, parts, and plans from Antique Ordnance Publishers all come from the estate of Paul Miller?
The next to last photo you posted shows cast tops/handles for elevating screws, and next to them are cast elevating screw boxes (only one is drilled). These are carriage parts; the elevating screw is set on the trail under the barrel breech, and rotating it raises/lowers the barrel.
The two large cast iron parts in the last photo, are lunettes for carriage trails. The lunettes are fastened on the ends of carriage trails, and are used to attach the carriage to the limber.