People have said they bored 402's to 427 but thats a shakey thing to do IMHO as the cylenders are too thin at that bore and core shift etc come into play. I would say not to do it because of all the time & money involved with a fairly good chance or running into trouble in the end.
But the old casting # 962 396 block from 1965-66 had thicker cylender walls and that block was used by GM for the 396 & 427 in thoses yrs because it could be safely bored to 427. This may have also been true for the casting #961 396 block from 1965-66 but i am not 100% sure of that.
Scott
