What James said about checking the timing curve.For what it's worth,my better Vortec headed 355's ran 34 total by 2500.That adjustable advance kit from Crane is a great choice.THE 262'S that I used were Comp Extreme units,but that Lunati should be just as good,maybe better by a little.Now as to that 268's vacuum,I see no problem what so ever there.Your headers should help,not hurt with either cam.