Most LS engines will take 7 to 10 psi boost easy as long as they are in good shape. I would start to be concerned once the engine got over 100k miles. Mostly piston cracking.
Thing is, a 5.3 with a good cam and exhaust is good for over 425 hp, about what a stock engine with 7 psi would give you.
Far, far cheaper than any turbo setup is a 6.2 with more cam and exhaust. 550 reliable hp all day long and more if you want it and it bolts right in place of the 5.3.
Seeing as how the 2v 4.6 is one of Fords most reliable engines, what are you doing to break them?