Question regarding value. What is a 1965 or 1966 Shelby GT 350 worth with a numbers matching motor? What is the worth of the car without the matching numbers motor? What is the value of the motor by itself?
Condition, condition, condition. I think what you want to know is how much an original engine adds to the value of the car. In a perfectly restored car it will add more than an original motor (needing rebuild/restoration) in a roach of a car. The engine (long block) sitting on the floor has no more value than any other HiPo - since it's the same as any other HiPo. The correct ORIGINAL aluminum parts and carb will add value. Of course you need to take the "numbers matching" hype with a grain of salt and do a lot of investigating since some restorers have been known to stamp correct numbers on the block.
If you have a HiPo with a VIN Howard can tell you if it was in a Shelby - but he won't tell you which one.