With different fender contours it would not be an exact fit
That is the car's fender tag. Go here to decode the numbers.http://www.stockmopar.com/mopar-fender-tag-decoder.php
due to the tightness in the engine bay inner fender well must be ground before installation
It will be on the right side inner fender well.
The horn relay on a 1970 Dodge Dart is typically located in the engine compartment, mounted on the passenger side, near the fender or close to the battery. It may be attached to the inner fender or the relay box. If you're having trouble locating it, consulting the vehicle's service manual can provide specific guidance and diagrams.
I doubt very much that the fender is the same as the darts.
yes
6
There should be a phillips head screw holding the light on, take the screw out and pull the light off the fender and then replace the bulb.
No
$5000
I don't believe you have enough fender clearance in the rear.