I didn't draw up the gun, this is the link to the ones I bought; https://www.shapeways.com/product/SB3L5GBCZ/3-pounder-x-4-1-72?option=40513481&etId=190519712&utm_source=automated-contact&utm_medium=email&utm_campaign=payment-received&utm_content=7
I cut the gun off the shapeways mounting post and stuck it at an angle on the kit post, and made the shield. It's not pivoted at the right point, but if you don't look too closely it doesn't show.
I've not found a picture that shows the top of the Seabrook, so I don't know if the drivers position was on the left or right. As an American chassis I'd assume the left but the drivers cupola is always on the right- did it slide across so the driver could get in and out?
I do have a 3D CAD program and have done some drawings. When you upload them to shapeways you get shown how they will look when printed, and costs for the different materials. All the drawings I did were for truck wheels, but they were too fine for the print process at 1/72 scale, so I didn't carry on. Did some castings instead. Wire wheels are even more fun, but not impossible to make from scratch.
Steve