Question above plus these.
Money?
Budget?
Money?
Budget?
That is what determines almost all power capability.
Not being a smart alex. Really only trying to help.
With a stock block 400 I would say that 421-422 is max. With a stock block 350 I will say that 396 is max. Yes' you can do bigger. I did a 440 cu in stock block 400 one time. I will never do it again.
Just like blocks and all other parts, cylinder heads come in all flavors up to over 20,00.000 and below. Blocks can go as high as 12,00 and as low as 200.00.
More info?
Ed