Pretty standard for LT1s. I rolled it into an oil change per Adam's advice. Switched to my usual GC 0W-30. I added 4.5 qts and I will have to check the level. These usually take 4.5 qts on an oil change but with the filter adapter R&R maybe slightly more came out somehow.
Other than removing the filter, remove the one 13mm nut holding the lines on an oil pan stud. Then you have to back the 15mm nut off that holds the oil cooler lines to the filter adapter. The nut was frozen on the stud so the stud backed out. Whatever. After that, two allen head bolts, 1/4". That's it.
You can see a little better here. This is the native block. Removing the gasket took just a little prying with a small screwdriver and it came out in one piece. It was quite hard. The O-ring was also pretty hard and squished.
On the left is the low oil level sensor. On the right is the driver's side front O2 sensor.
Oil filter adapter. I cleaned it out before putting it back in just to avoid getting dirt and junk in the engine.
Old gasket and O-ring.
I torqued the bolts to 18 lb-ft which seems high but it held. My 1/4" allen drive socket wasn't really long enough to get a good grip on the bolts. So I hacked off the end of a 1/4" allen wrench, stuck that into a 1/4" socket and used that. It worked great.
I did inspect the oil cooler lines while I was under there. They aren't bad at all. I didn't really see an active leak, so it is fine for now.