I have what looks like crankcase gases escaping from an app. 5/8" hole in the drivers side lower timing cover just behind the harmonic balancer on my GM goodwrench 6.5. this is a 6.2 retrofit project I picked up as a basket case so I can assume nothing was done right so far. My 82 6.2 has no opening at all at this location so I am guessing this is the place a TIMING SENSOR might go? the bore of the hole is smooth. Any ideas?

Sounds like the hole for the CPS, you could probably use an old CPS to plug it.

Thanks Rigger, I figured as much, just needed a little reassurance. I might just put one of those expanding rubber freeze plugs in it since I don't have a CPS handy - I imagine it would hold up ok, what do you think?