Well all I can go by is my experience from 2-1/2 years ago when our 68 bird was rear ended and wrecked pretty good. I offered the car for sale complete (drive train and all) for 10k and what I received was a couple of low ball offers for 3-4k. So I then decided to part the car out and did so. I parted the car out for 13k and kept the motor and trans. Just a couple of months ago I sold the motor for another 5k. The trans in in my 67 LeMans and is worth at least another $2500 due to the fact that it had been completely rebuilt just prior to the bird being rear ended. Then in addition I traded 3k in parts from the bird for parts for the LeMans. Plus, this did not included the repair money from the ins. co. (Hagerty) from the accident itself.
So as I learned from my own first hand experience you can always make more parting a car than you will getting low balled by someone else in the hobby. Had someone bought my car for the 10k when I offered it, they would have gotten a 10k drive train alone as I had one killer 400/4-speed/3.55 rear combo that was all completely rebuilt, and built with nothing but the best of everything top to bottom front to back. From steel ram air pans to long branch manifolds. The rest of the stuff such as bird glass, fold down seat and darn near every OEM option available would have been the icing on the cake for the buyer.
I am now in a similar situation with my LeMans. We may be buying a home. The house has been gutted and needs all the interior trim (carpet, doors, trim moldings etc.) we are getting a great deal on the house but we would have to sell our LeMans for the money to finish the interior.
Well, in my opinion the LeMans being a 100% rust free, ALL original sheet metal car, 90% original paint, ALL original interior (that is basically perfect a 9 out of 10) and with the OEM options that I have put on the car ie: tilt wheel, red fender well liners, rear window defroster, power seat, power trunk release, rear power antenna, and the list goes on. I feel the car is worth 20k. Here again I am being offered 15k etc. Now I realize this is rough economy etc. however, I know for an absolute FACT that I could part this car for well over 28k without any question in my mind.
Now do I want to part out a completely perfect 69k original mile 67 LeMans with it's original: motor, rear end, interior, original paint, Rally I rims and 5k in OEM options, 5k aftermarket upgrades ie: 4-wheel disc brakes, original AM radio conversion with single front & rear speakers upgraded to dual voice coils for true stereo sound but yet maintaining it's 100% original bone stock look but having 80watts of power and sounding like a modern sound system. Diamondback red line tires. Stainless steel brake lines and the list goes on and on.