Re: volvo penta aq130c and 270 outdrive
There are just too many variables to give an honest value. I paid $200 for an AQ130C this past summer but you may or may not get that much for yours. If it's actually running, that's a different deal. If you can prove that the head isn't cracked and that it has decent compression, you may be able to get 7-800 for it if you can find someone who needs one. But you're not going to get good compression readings until the rings reseat, and that involves running it for awhile.
It's getting harder and harder to find those engines complete and in good shape. Unfortunately, it's also getting difficult to find boats that old that are worth repowering. I would think it's worth putting it on Craigslist or even e-bay. Take a look at ebay and see what others are asking for the components. You'll see some engines and parts there for a very long time and it's easy to see which ones sell fast. Hint - it's the ones that are listed at a reasonable price!
After just rebuilding one of those engines, would hate to see one go to the scrap heap.