I agree with the badge being correct for the car. Era-wise, though, not necessarily displacement-wise. If the car came with a 5.0 badge and you stroke it, personally, I'd leave th 5.0 badge. For one, why tell your secrets to the opposition? Let the other guy think he just got it handed to him by a 302. Second, It's what came on the car and is factory correct. Incorrect badges or badges where they don't belong to me looks silly.
The new 5.0 badges are attractive, I just prefer the origional equipment look trimwise for my steed.