I know of a twin turbo 455 that went about 15 years without a rebuild. Used it every other weekend every summer. I have allot of faith in the OLDS. Another buddy has run the heck out of his olds for a few seasons. The only thing (I am sure you heard and know) is to not rev it to long as the oil stays in the top end and it will starve the mains and uh oh. WHY CHANGE THE PERFECTLY GOOD MOTOR!? YOUR NUTS lol just trying to save you some hastles and $$$