Engine is worth the most as a lump if it's a good one, and I think a complete engine is worth more than it's parts. As for how much it's worth, it all depends on how far you want to go. But I don't think that a Discovery is worth as much as you think as there are so many of them about. But if you price the bits cheap enough, strip as far as you can I would expect to see about 600 for all the bits.