Originally Posted by Redsteel
Is a 40 over bore too much to mess with?
.040 oversize bore is .010 past what the factory recommends for a stock 351W oversize bore.
However if the block experienced minimal or no core shift when it was cast then it should be ok.
Core shift can be "eyeball evaluated" by observing how well the freeze plug holes in the sides of the block are centered in the bosses cast for them. As long as they are pretty much centered, I wouldn't be overly concerned about the .040 over bore.
Just be sure the bore is square and the finish is correct as you don't have much room left for any corrective machine work.
P.S. I have tried up to a .060 bore in a SBF that exhibited no external evidence of core shift, but that left me with an engine that easily overheated due to the very thin cylinder walls and I doubt it could have withstood much abuse without disintegrating under the pressure. Driven granny style in an old Mercury Marquis, it did survive for just over another 150k miles though.