WARNING: This page is about a different car, the 2008 Buick LaCrosse and 2008 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: View Of 5.3 Liter V8 Engine
Courtesy of GENERAL MOTORS CORP.
The 5.3 Liter V8 engine is identified as RPO LS4 VIN C.