Here are more photos on the main cabinet structure repairs, along with the backbox.
Then the Bondo repairs are needed to remove the decades of bumps and bruises.
The backbox had a major hole around the lock, looks like the key was lost, and drilling through the cabinet allowed someone to reach in with a tool, and unlatch the backglass; personally I would have drilled the lock.
This Bondo repair will have to be reshaped , and smoothed with a dremel, as it cannot be reached with a standard sander.
Also here, I’m going to focus on how to properly repair the riser.
The riser is the plywood structure at the rear of the main cabinet that the head sits on, it takes lots of abuse, and is under built for the age of this equipment, and the on/off cycles of the head it has been asked to endure.
Most are loose, and falling apart, one major contributor to this is transporting the game with the head attached. Don’t ever do that!
It too heavy, it will sway and wobble as you hit bumps, turn, etc, which will start to tear apart the riser, and actually rip it off the main body.
The riser it’s self is held together with air staples and glue. It is affixed to the main cabinet with 3-1/2″ nails, which need to be removed, and replaced with modern wood screws, if you want structure back.
And, I will also show one way to repair the main cabinet bottom edge, which due to carelessness over the years becomes chewed up, and the bottom board starts to drop out.
So flip through the photos, it may help out with your situation.
Live long and prosper!