I would paint it. By not painting it you're trying to attract two different crouds in an ineffective manner. One crowd wants to do it yourself. But you've already got the motor done and it only needs paint... They're going to want to know what went into the motor, and will wonder why you want to sell it. Then there are the guys who really don't know to do that much, but will see the paint, the chrome and the pretties and want to buy it, thinking you've spent years building it.
I would paint it, and sell it to a doctor.