74 Gold Duster and tons of questions

1) 340's and 360's are physically identical on the outside and even take the same motor mounts, so you're good there. The transmission will work with either. you just may need a different flexplate or knock the weight off the torque converter. It's hard to tell what your rearend is without a picture. Does it have a cover on the back? If so, how many bolts does it have?

2) I would stick with the 360. They look identical on the outside...I'm not sure why anyone would slide under the car and look at the casting numbers on the side of the block

3) You would have to change the hood, front fenders, filler panel, and bumper

4) That scoop came on the Dodge Dart Sport or the Dodge Demon. You can get aftermarket reporductions

5) You can remove those if you want and only a slot will remain. A 73 front bumper won't have that if you keep the same grill structure. For the rear, you could use a 70-73 rear bumper and the right bracket

6) Yes, Order stripes for a 71 or 72