My neighbor, who I often refer to as having a small boat with a new engine and this and that, is having side rails and a radar arch with rocket launchers made at a local welding shop for his Boston whaler. It's costing them a little bit of money, but he's getting exactly what he wants. That might be the way to go. get a picture of what you're looking for, even if it's a different boat, and then go shop around different shops and see if they can make you exactly what you want. Probably better than adapting and off the shelf product.
I know this is a late reply, but assuming it’s still in my closet, i’m willing to sell mine , cover and/or ladder to anyone for the price of shipping. I moved away from saltwater, and installed a trolling motor in the ladder space.