Here's the scenario I have a 1969 L78 854 casting 4 bolt 402 block that has already gone .060 over at some point in it's history. One cylinder now has a deep gouge due to a piston pin that walked out and wore into the bore. I am exploring the idea of boring the cylinders to 4.250in which, with the correct 427 crank, rods, & pistons, would bring it to a 427 cubic inches. Using the internet I've only began scratch the surface to whether or not this is a reasonable decision. Out of a couple dozen threads I've come across only one where a guy did bore a 402 to a 4.250in and reported it runs fine with no overheating or sealing issues what so ever. Those who do make comments say before boring have the block sonic checked before, others say use the #2 pencil technique by removing a core plug and try placing a #2 pencil between the cylinder bores essentially a go no go gauge. If it goes the bores were cast to thin if not, then proceed with a good machinist.

Has anyone successfully (or not) carried out this machine work? Any sound advice would be great.
Thanks
DC