Zero offset on 14 x 7" rim wheels for P245 60 R14 on stock 1969 Dart, anyone could tell???

All factory 15 x 7 rims have a B.S. of 4.25. Those seem to work well on most Mopars including a bodies.

Because your suspension is removed from the car.....can you mock up the new tires/wheels on the ground?
Put them in place with the body dropped down over them. I'd leave about 1.2-1.3 cm between the outer tire bulge and the quarter panel lip. Then carefully measure between the mounting faces of the wheels, left to right. Compare that measurement to the ovrrall wheel mounting surface dimension on your rear brake drums.
That should tell you if you have a chance on fitting these.