Aluminum motor's have steel sleeve's in them!
My navigator had an aluminum block I had it for 5 years 80k miles never waited also no knock or noise.
:shrug:
Is it just the new GT500's that get the plasma-transferred-wire-arc spray on the bores? Thus making the iron liners unnecessary. I'm certain I've read this for the GT500's, but not 100% on the 5.0.