It's in the bottom end for sure... i hooked my dad's scanner up it at least shows 55psi cold on the oil pressure. Time to start pulling it. Trying to make a list before hand, however who knows what i'm going to run into.... im figuring crank, bearings, oil pump, gaskets... then ive gotta figure out the whole dod delete... that's a whole other list of valve train trinkets....
Holy crap are you going to have a bill of a life-time. At that point I think it'll be cheaper for you to just go find a used L99 and swap that.
But on a serious note I think its the lifters getting poopy. Mine has been making a knock like noise at startup for 2 years now. If the car sat for a while it does that. Or if ambient temp goes below 45F. It's the hydrolic lifters that release oil far to quick and don't store any. So once you go to turn the car on they tap/scrape the camshaft causing that noise.
Best way would be to look at the oil for shavings (mine has some metal specs in there every once in a while.) But no tick yet.
Oil pressure on L76 is going to be 'Weird' because of DOD. Once it goes on it'll read lowish; At first I thought same as you, then when I went to various engine forms and found out that the system tends to run at lower pressure than normal LS when DOD engages, for example I have oil pressure gauges on mine and its hilarious to see the oil pressure dial jump back and fourth at idle because of DOD. (One of the few ways you can tell its on.)
If the oil pressure drops too low you should get some sort of Error/Check engine code pop out. System should do it automatically once you go below 10KPA (15ish PSI). On cold start, high oil pressure is normal it'll drop once everything warms up.
Example: (My gauges are aussie so my readings are in KPA) At startup my engine reads around 450KPA (65PSI) but once it reaches operating temp it cruises at 200 Kpa (29psi). The funny kicker is that once I pull over and idle at about 550rpm the pressure jumps from 150Kpa (21psi) to around 200Kpa (29psi). And goes back to normal once I as much as breathe on the gas.
One last thing. In your owners manual it should actually tell you the threshold on the oil pressure (I believe on LSs 30Psa on warm oil is normal). Oil pressure should increase I think 10 psi per 1000rpm.