This probably explains why your engine guy is recommending the 284. Again, being carbed (and like the demons too, Bary Grant knows his stuff) I wouldnt see a problem with the larger cam. Just depends on what your after.

If you are looking for gas mileage, the 268 would be smart. But if your like the most of us horse power freaks, the 284 shouldnt be too big and will give you the head-turns when you crank it up.