Top end or bottom end
If you are seriously considering going with nitrous, I would go for the bottom end first. I would probably go with the bottom end anyway as I have lost more engines due to bottom end failure than top end failure. I have run a 377 and was happy with it until a rod bolt broke. It was an ARP bolt and the next engine was run with ARP but beefier 7/16 over the 3/8.