Re: 1961 14' runabout
I would return the hull to it's factory height transom. It's already cut, so the outer glass or cap is already compromised to some extent. I'd make the new transom full height, glass in the missing areas and make a good solid aluminum cap for the transom area.
I had an older Starcraft which had the transom cut, I replaced the wood, reinstalled the cap, filled in the missing glass, sealed the top and took a section of 1/8" wall 2x2" aluminum tubing and cut and machined it to fit. I simply removed one wall of the tube on a table saw. The motor had no problem clearing the extra width and it looked great. I also added a polished outside motor place that was just larger then the engine bracket for extra protection and to eliminate any intense body work blending in the patch.
Inside the splashwell I simply smoothed over the repair flaring it into the existing glass work. I also moved the splashwell drain to the side.
Although there are some benefits of a motor plate, they do add some stress to the transom and are costly. It can be a way to gain power tilt and trim if your motor lacks it though.