The 5.3L blocks are unique in the way that they can be bored out so much. I too thought that 3mm of bore increase was waaaayyy overkill, but that's because I grew up with small blocks only receiving .030" and .060" over.

 

yea I was the same way that is why I asked thanks for clearing that up

 

A sonic trest of the bore's wall thickness is the only sure way to go. On the other hand, I haven't read of any 4.8/5.3 blocks punching through the cylinder when going to 3.898"/3.903"/3.905".