I have a friend that is building a 557 with Trickflow a460 heads and intake and will be running a 250 shot of nitrous would a 4 bolt main block be advisable?

This is going in a '65 1/2 ton 2 wheel drive.

 

If he has the money I would go for it. It really depends more on how high he'll be spinning the engine rather than the use of nitrous. With a set of Trickflow A460 heads and all the roller cam/valve train goodies he'll be able to make power in the 7,500 RPM range...and with that extra long stroke you'll definetly want the piece of mind a 4-bolt block will give him. Word of caution though, I would not use an off-set ground cast crank in this application...

Deen