Yer killin' me here...cuz I don't understand this stuff & I'm curious....what's a stretch bolt and why shouldn't you re-use the bolts? Already stressed? Is all that black carbon/soot "normal" or should those 1st pics posted be much cleaner?
OK, I could look this up on the intent but you all are more fun...

Newthings....My background is kinda similar to yours in failure analysis, except my expertise was in healthcare...investigating when medical things fail or go wrong....surgery, medications, instruments, human error....etc... so I'm like the National Enquirer.."Inquiring minds want to know".

And Fuddy can you trust that book? My mechanic has a reference book that says our 3.5 engine IS an interference engine...when the pros here says it is NOT.