Every 70 Dart hood I have seen, even slant six cars, have the cutouts and openings in the support structure for the twin scoops.
Are you sure this other hood you have is for a 70? It should have holes in the front center on the hood for the chrome Dodge script.
Also if you have a twin scoop hood you should be able to measure off of it to recreate the openings in the other hood.
The extra hood I have is from a /6 70 Dart I used to own. It does have the Dodge emblem in the middle and it was the original hood on the car. It is buried in the garage right now but as soon as I can get at it I will post a picture of the underside so you can see what I mean. I am not referring to the holes for the twin scoops but rather the holes where the studs would go for a dual snorkel.
