74 Dart only starts in neutral

It likely needs adjustment. Go to MyMopar (for now) and download the 73 manual. It tells you haow to adjust the linkage.
I agree. It will "look" correct but like someone else said, the bushing may be worn or whatever. With it in park and not wanting to crank over, get under it and move the linkage in the direction that it would be moved by the park gearshift lever. If it move further by hand at the transmission and it starts after you get back into the car, then the adjustment is off.