75 valiant build, go back stock /6 or v8

So as most of you know I picked up a herd of 1975 Plymouth valiants. The pair of 4 door parts cars and the 2 door one. Well, the 2 door was advertised as you know with a v8 and 904 transmission. Well, I was talking with the last owner about picking up the engine from him this week and if he had the back glass. Then he mentioned that the car was an original /6 car........"wait, what". I had been under the impression it was a v8 car. So my two questions are: the two parts cars I have are 1975 /6 cars, so I use one of those for going back in the 2 door cruiser or Schumacher v8 kit and 318 or 360. Second question: does the back glass from the 4 door car work in the two door? As I have two good ones in the parts cars. My wife wants to go with the /6 to make a gas saving cruiser and paint the car 2018 dodge ruby red. Flat black dual snorkel hood scoop and black band around the back trunk and quarters.