Just my 2 cents worth. I know this has been a budget project for your family to enjoy. A wise old friend once told me an old boat with a motor and trailer is worth $300. You put hundreds of dollars, and hundreds of hours into it, and it's worth $300. I don't think it looks good, but I don't think it looks that bad. You're not putting a big motor on, so there won't be a lot of strain on the transom. I would put a 1 1/2" aluminum angle across the top of the transom and run it. If you get a couple years fun out of it, you can decide what you want to do. I don't think it's unsafe.