Don't rush on the decals, think about and talk to a lot of people and you will have that AHA moment on what is to do best. That being said I would change the wheel and add the wipers and then not do anything until you drive the car for at least one summer and get that out of your system. You will have the car the rest of your life so what is one summer. You will get more driving pleasure out of the car knowing it is ok to get the engine bay a little dirty know that "next" winter you are going to redo it. Again, giving you more time to think about and get feedback from others. The decals for now will be a cool story at shows to tell people the original owner put them on back in the 70's, enriching the story that is a 1 owner car. Like people say about cars with non matching motors the decals are "Correct for the time period". Great car, great story.