Old Z's are notorious for getting light in the front end at speed. Too much air gets up under the hood at speed. The grill opening is way to big with no where for the wind to go. If frame rail strength worries you about the differences between the 240 and the 280 just add big dog fame rails. That is the biggest difference that I have noticed between all my Z's. As to the wind under the hood I have seen it mentioned a number of times in the forums. Do you have a front spoiler on your car now?