I have one just like this and it is pretty awesome gasser. I pulled out my manual and it apprears that the bottom panel can be ordered separately. It is hard to tell from the pictures the true condition of the doors. The flavorizer bars look to be in good shape. How are the burners and the igniters? Turning on the high heat and using a brush is good for normal maintenance, but you still need to periodically do a more thorough cleaning to prevent build ups. The Summit hits some really high temps and burns most stuff up but it doesn't get everything and builds up some crud over time. If it were me, I would do a good deep cleaning since you are going to be pulling it apart anyway. Good find. Hope you enjoy yours as much as I do mine.
WSM, 2 -Performers, 2-OTG, SJG mini WSM, Summit 420, Q100, KJ Classic, KJ Jr, and Schwenkgrill