Well Josh, That is a tough one....
If you told him you would do it, one side of me says just keep your word... you will find no fault in yourself this way.
The other side of me says "right is right, wrong is wrong" ... if he told you it was turn key roller, then it should have been turn key (not in need of a shifter, reg, lines, trans cooler, etc...).
Here is the big question: Did he lead you to believe that the car was in need of nothing? Then later you discovered that you had to replace all of the parts? If so, I think I would keep the delay box. You are replacing the parts because you have to... not by choice? (I understand you have no choice to replace the belts)... but was the shifter/reg/lines etc.. bad?
You seem to have made it clear in the ad that it did not come with the car as a roller... only turn key w/ motor... right? if so, I see no reason why he feels HE IS OWED the delay box if you made that clear. I guess I would weigh out this whole thing based on his honesty, attitude, & integrity before I made a final decision. Scooter