If engine is running well as you said, for $500 I would buy it. The injection pump alone would be worth that on eBay! If you have the time and patience parting it out could yield ~$1k-$2k. Zero risk of getting $500+ since there are plenty of parts to harvest.
Of course you're really wanting a working generator in the end. There are multiple things that could prevent unit from producing AC output. Could be something as simple as the AC reconnection switch contacts not making good contact (NEVER EVER turn that switch behind the panel covering it while unit is running!), bad rotating diodes, exciter issue, bad Voltage Regulator board, loose wire, bad transformer, fried component on a board, and on...
If you were to purchase the unit members here can suggest easiest to more complex tests to perform to find out where the problem actually lies. There really is no one test but a series of elimination tests that can take a while to run through.
One thing you could do is post good pictures here for members to assess the units over all condition as a first step. I would focus on the gen head, control panel inside & out, AC reconnection box and wiring harness as a start. Since the engine is running well maybe just a couple of shots of it. Also a shot of the MFG placard with date would be good.
