302 heads-Is it worth putting them on a stock 318

To me it would depend on the shape of the heads already on the car. If your compression checks good and pretty even across all 8 cylinders, then I would suspect you have good valves and I would leave it alone. If your needing some valve attention, I would get the "other heads" done up (including a little bowl porting) and that would speed up the car's down time.