There isn't enough weight difference in the heads to worry about. The AIR holes are a moot point. Plug the back hole where the line used to go and call it a day.
The '75-80 heads do not have a big enough pushrod hole through them to get the lifters out if you change a cam in car though. The '81 and up heads do, if you have a steady hand. Other than that there are no drawbacks to the later heads.