Yes
they should fit as it's the same body.
yes, they are the same exact cars the only differences are the front headlights and grill and the tail lights otherwise the cars are pretty much the same. so yes, a 73' nova hood will fit a 70'
No. The subframes are not the same. The 68-74 had the steering behind the crossmember and 75 and up had it in front of the crossmember.
not without modification