I've wondered the same thing but I don't think this guy trully knows his way around underneath the hood, I suppose I can ask though. I'm buying this car from a distance, otherwise it'd probably be quite easy for me to inspect it and find. Here is his exact words...
The transmission has always had a good solid shift and I was concerned at first because it was so firm when shifting into gear. (the whole car settled down into gear) I was told by both owners of other cars like this and mechanics that was a character trait of this car. It just jumps when you put it in gear. Now, after the accident that "jump" is considerably more pronounced and the accelerator does not move the linkage properly when the gas pedal is pushed. Basically the car will not go because the arm to the carberator does not move far enough to actuate the throttle. I have had it looked at by a backyard mechanic and he thinks the violent shock of the rear-end crash broke a motor mount and that explains the change in transmission jump and the lack of linkage movement in the throttle.
Re-reading this it almost seems as if he himself watched the linkage not move, by the way he worded it. Also he implies either the motor or tranny are under a bind now. It's kinda like stabbing in the dark without being able to see what is going on.... Thanks for the suggestions, keep them coming. :-)