You can't bore a 425 to 500. you're lucky to get it even 60 over. The 425 block is also lighter weight than the 472/500 blocks. They supposedly removed the weight from "unimportant places". As for all this talk about the 425 crank, I had a discussion with Al at MTS about that when I first took on this project and he was saying that those cranks are not as weak as some believe. He said his expierience was from racing them and most of the talk about the weakness of the crank was coming from bench racers. Me, being new to the world of Caddy motors, took his word for it. Hard to argue with a guy that has one of the few speed parts places for Caddy motors in the whole world. But, as for nitrous, I stayed away from it in a 425 also.