A 16x40 wheel likely refers to a 16-inch diameter with a 40 offset, which may not be compatible with a 1973 Nova. The Nova typically requires wheels with a backspacing and offset that accommodate its suspension design and fender clearance. It's essential to verify the specific measurements and clearances of your Nova, and to consider tire size as well. You may need spacers or different wheels to achieve a proper fit.
No
not without modification
Fitment depends on the width AND offset. 18x8 +40 will fit.
Yes.
Yes it will bolt right on.
No, they are 2 different bodystyles
Yes.
Yes!
It should as it's basically the same body.
If it is the same bodystyle, yes
yes they will fit you just need a 8 or 8.5 inch wide wheel with high offset. the offset is very important if it is to low they will rub. 8 inch wide wheel i would go no lower that a +35 offset and on the 8.5 wheel i would go no lower than +38 offset.
Not without modification. The 1973 and 1974 body styles are unique in the Nova series.