It is harder than you think and get it correct.
The difference was back in the days it was somewhat easier as there was only one cam and a lot less chains in the motor. Plus the bump in compression was also minimal.
Now with variable this and that as well as everyone has decent compression ratio it is not needed as it is not cost efficient. Plus when you start messing with the geometry
of the heads and stuff you mess up the geometry of everything else happening inside of there. You might end up with too much slack in the chains, might have to mill the
intake manifold as it is not fitting correctly, maybe the timing cover will need adjustment, you will also retard the camshaft a bit by decreasing the clearance.