To the best of my knowledge, there are no literal step-by-step threads on replacing the plenum on a 2000+ Northstar. That's the realm of a GM Helm Factory Service Manual or a subscription to
www.alldatadiy.com.
You remove the beauty cover, disconnect the fuel rail and FPR vacuum line, remove the fuel rail, loosen the plenum clamp, pull the manifold bolts, remove any vacuum/supply lines necessary, lift the manifold, unbolt the plenum from the throttlebody, clean the throttlebody, (forget trying to clean out the oily deposits in the manifold), check the starter cable connections, install the plenum, use new intake gaskets, oil the lower fuel injector O-rings, and put it all back the way it was.
Here's what you're after............