[carjmark]

IMHO, key part of value is also whether you're talking about a core/unknown motor that buyer has to assume the worst on and total rebuild vs. rebuilt and documented by quality shop (or something in between). With a core its what's the premium someone's willing to pay for a "S" stamped case (pre-injected) versus standard, with rebuilt its that plus rebuild cost/value.

Also factor in whether motor is complete w/carbs, oil cooler, tin, heat exchangers, flywheel, distrib, etc. vs. longblock that can add/subtact a couple $K. As an example, paying $9800 for a complete motor then spending $12K to rebuild is an underwater adventure unless it's serial # matches your car. Too many estimates seem to ignore these obvious variables.