1st time shell buyer, need advice/input on a used Leer 100R (1st Gen DoubleCab)

So I have an 02 Double Cab with a Toyota over the rail liner. I want to add a shell and have found one on Craigslist. Pics of shell below - owner asking $500 for it. Missing window screens and something about the locks not being 100% solid. So here is where I am at:

1. Its a Leer 100R

2. I realize it would be ideal to remove the factory over the rail liner. I removed the liner and it was a mess under it. Installed 14 years ago and I have to say, it was dirty and had a few rub spots down to the metal but overall the scuffs buffed out and the paint looks better than the exterior. I looked into a Bed Rug but apparently they dont make one for the short bed. Not sure what to put in there so suggestions are welcome. Definitely want something to protect the knees and make it comfortable if my kid or wife want to lounge back there.

3. The screens shouldn't be bad - hell, I can re-screen anything so long as the frame is there.

4. Locks might be an issue - please see pics and comment.

5. Shell has Yakima tracks in place - I want to go the route of a basket so I need to figure out what additional hardware I would need. I've been told the tracks will take either Yakima or Thule crossbars(?)

5. If I decide to buy it, I was thinking of having my local dealer redo my install (from getting it home) - thoughts? Local dealer quoted $85 bucks for the re-install (includes new seal, etc).

Never owned a shell hence the q's plus figured if I posted actual pics you folks could give me some advice.

Look like a deal @ 500 with the work that needs to be done?

Thanks in advance!