If you're experiencing antifreeze in crankcase I would recommend not running the engine at all. I don't believe "additives" will help at all. Main bearings may become damaged resulting in more expense to repair. If running and coolant is expelled or low it will overheat quickly and could result in lower intake manifold warping.
At and after 80,000 miles it appears 5.7 li VIN R v-8's are prone to lower intake manifold gasket failures. Usually any or all three types of leaks may occur: into crankcase, into combustion chamber and external.
FelPro MS98000T intake gasket sets are metal/rubber vs factory plastic like material and appear ideal to seal especially if minor surface irregularities on lower manifold to cylinder head surfaces exist (possibly from corrosion).
As mentioned, it is critical to index and mark distributor so when putting it back in it is "exactly" in same position as before removed. It will throw error codes if not exact. (Something like 2 degrees leeway)
Might consider taking lots of photos before and during tearing into it. It definately helps on reassembly.