Nick,
You would be happy with the performance and the sound of the 2 1/2".
Yes there is a 455 crank that's available to fit the 400 block. I believe you would need to bore your 400 .030 which is a standard 455 piston size. You would need a new crank, pistons, rings, and probably bearings. Might as well throw in a new timing chain while you're at it. But with machining and parts you're looking at close to $2,000.
It looks like you've already got an awesome set up. Especially with the 722 heads. If I was you, I'd save my money for a 455 or 474 build up somewhere down the road. Once you have the cubes, there's no going back!
