I am researching this as well. Moroso lists sheet metal and cast VC grommets to accomodate the thickness.

The specs are 1.25 OD and 1/2" ID for the PCV (GM used 3/4") the breather is 1" ID (the K&N types are 3/4" ID)

I'm not going to run baffles, so I'm going with the integrated type

grommet list