The real answer always hinges around finding someone who's actually got money in hand and intent to buy to agree with whatever valuation you settle on. A seller will most often think in terms of...."well, I spent over________to put this combination together." The buyer always wonders "why would anyone take out a good engine.................hmmm, I wonder what's wrong with this?" Which is my long winded way of saying it's best to sell the engine from a running car, or on a run in stand where compression, cooling, and all the rest can be demonstrated. A lump sitting on the floor with the typical admonition "It ran good when removed." only works when the buyer knows you well enough to trust you.