Yeah, here's the deal.

Base engines sell fairly well. Bare blocks sell fairly well. Hell, used engines sell fairly well.

Built engines sell even better, if it's a customer/builder type relationship. Built lower ends sell even better, but again, the best $$ is found when it's a customer/builder relationship. Built, used engines DON'T ever sell for what they would cost to build, or even a few hundred less, they sell for considerably less because there's no reasonable expectation that an engine like that would have been found in a granny's sunday driver, and abused engines are like a psycho girlfriend that drinks gas. Sure, you have a [girlfriend] engine, but how long do you really want to put up with the issues that come along?

That said, I learned early on not to build an engine and then try to find a buyer, you find a buyer, and then build an engine, because people are more willing to drop several thousand if it's exactly what they want.