Will I kill the value of my Demon

Really I, wrongly, assumed since the fender tag had d34 and said light duty automatic transmission that was the a904

I would research the whole car at this point. If that's the correct fender tag and it does have D34 as the transmission code, the car is not an original H code car. D34 designates the 904 transmission which 340 cars never came with. I would get to the bottom of this before you buy.