Cut transom brace replacement

I purchased a boat recently that I am excited about because I was looking for a wider boat. However, I am realizing that I need to do more work than I expected and I need some help. The people that owned it at one point had to replace the transom and apparently just cut the braces off. They probably didn't need them because they were running a trolling motor, but I am putting a 9.8 on it. It looks like someone may have already done this after they were cut out due to the cracks on the transom (see pics). I am getting a friend to help with the welding of the cracks (one quote was for $350), but I need to come up with some new braces. One idea I had was to run an L bracket from what's left of the brace to another L bracket I would put on the transom and put a bolt in either side, but that might still allow for flex (see image below with red being L bracket and blue being bolts). Another option would just be to run two L brackets from the back seat straight to the transom. Suggestions? I only paid $600 for the boat and trailer so I'm not looking to fix it as inexpensively as possible. Some pics are below

Welcome back to Tin Boats!

If your transom wood needs replacement, now would be a perfect time to do it.

What you call L bracket I'm going to call aluminum angle.

Instead of angle from the old cut off knee braces, I think I would use thick aluminum sheet (3/16 or 1/4) cut to shape (like the white outline in the pic below). If possible, get your buddy to weld it to the cut off knee braces (I'm not a welder so don't know what if any issues). Then connect it to the transom using a piece of angle. My two cents.

I just noticed the filler piece under the transom cap (see arrow). That does not look right to me. I am going to assume the original transom wood was the thickness of the current transom wood and that filler, maybe 1.5"? Here is what I think -- when the previous owner replaced the transom I suspect they used a single thickness of 3/4 wood or ply then used that piece to fill the gap so they could clamp their trolling motor.

I am sorry to say I think you need to get the transom wood to the proper thickness. There are a lot of ways to do this. Some use a couple layers of exterior plywood glued to gather to get to the needed thickness. If there is any good news, it will be an easy job right now because the knee braces are out of the way.

Yup. Pull the plywood, use it as a template, and double it up. Put it back in, make up a brace, rivet/bolt and you should be good.

It amazes me what people do to boats. Why anyone would even consider cutting off the knee braces is beyond my imagination.