Rule of thumb on the Pre cup cracks is that the length of the cracks should not be more than 3/16 long and can not cross the fire ring of the gasket.
If you have cracks that are 1/4 inch long its time to be replacing the precups.
Be sure that any cups you use fit properly (need to be no more than .002 above the head surface and not below the surface) These can fit with a light tap fit but some will fit looser.
If they fit loose a light staking in two places to be sure they dont fall out when installing the heads is fine.
Be sure the precup pocket is very clean before installing cups.
There are a buttload of different cups out there. Most GM originals will fit and work.
The Diamond cups are the latest incarnation and have the largest port.
There are ones with a single round dot, a single square dot, A large T.
The 6.2 had several different ports too but, they are very small ports and are more suited to a mileage getter rather than a HP maker.
To remove the old precups, remove the injectors and the glow plugs fronm the heads.
Using a hard wooden dowel, insert the dowel though the injector hole and tap the cups out with a hammer.\\
When replacing the cups, insert the cup in the hole so that the index notch lines up and then tap the cups in using a soft hammer only.
Again be very careful to have the cups and the bore in the heads very clean. There are sharp edges that can't have any carbon under them.
Hope this helps
MGW
