Not a 8.1, but my last gas chassis coach had the 454 engine. Purchased new in 2000 and traded in 2008, operated for 84,000 miles. That thing used one quart of oil per 1,000 miles from day one until it was traded.
Per GM specs, that was on the low end of acceptable, but was not cause for alarm.
In the overall scheme of things I guess I can say that I spent about $300 for make up oil over eight years. Didn't break the bank or blow the engine, so all was good.