Do you plan on dropping it in as-is or do you plan on going over it (inspection tear-down) first?
Depending on local, $500 could be a fair price. If I trusted the yard I would pay that. But I would also try and knock off a few bucks for missing items. A/C compressor (I know you probably not going to use it, but it is leverage to work down the price), the remote TFI module (good to have since it has a roller cam distributor already but is just missing the module), cap and rotor are missing. Try offering $300 and work up to $400. But if you have to do $500, and the local market is slim pickings, looks like $500 it might be afterall.
I would make sure the crank still moves (just to make sure it isn't locked up) and check the stretch in the timing chain (since they already have the distributer off for you) to see if the 64k feels right.
From what I see it is a clean engine, doesn't look like anyone has been in it before either. All good signs.
I would keep the EFI stuff, little pieces come in handy when doing a swap later. This fuel rail has issues here, but this other one works. This different heater nipple works better. Better to have a selection of parts.
For $500 I don't expect the seller to open the engine up for you. If you really want it tore down and look for damages I would expect the deal first, do the tear down and come back if there is problems. If I was selling it and you wanted me to tear down a complete engine so you could decide if you want it or not, I would tell you to go pound sand. There are others who would want a complete engine ready to drop in that will buy it. Yards sell complete engines, the last few yards I delt with would not sell heads off an engine. They want to sell the complete engine. They have a hard time selling a short block, or even storing one. Most normal people wanting to get there ride rolling again simply want a complete engine to drop in, not have to put one together. When my grandmother lost compression in a cylinder due to lost coolant I just found a junkyard engine and dropped it in instead of trying to figure what was wrong with the old one. I would not consider an engine from a yard that had it tore apart for inspection, last thing I wanted was to build another engine from used pieces.