A lot of the buick guys put an inline check valve above the stock pcv to keep it from blowing boost pressure back into the valley. But the stock GN PCV is supposed to close off under boost. You should be able to buy a GN pcv at a parts store or the buick dealership.
However having only one breather for your vent may not be enough.
You can try these first and if that doesn't work you can do what I have done.
I bought a moroso aluminum vacuum pump canister from jeg's and will run a -12 line from each valvecover to the canister. I just had to buy an extra aluminum -12 bung to have it welded to the canister. The thing I like about getting the breather off of the valvecover is the oil from the breather doesn't drip down onto the valvecover.
If you didn't want to add an additional bung to the canister you can also just T the -an lines together and then run them to the canister. I chose to run two seperate lines to make sure I vent enough pressure.
