621
My 622" had 14.5 degree EPD/Brodix Pontiac style heads with 460 CC intake ports that flowed 480+cfm and 2.45" intake valves.
On a true Chevy Head RFD/Edelbrock heads are some of the best flowing.
That being said, if I already had a good set of Big M 410 cc heads, I would perobably use them if the pistons were compatable and then get a custom cam designed for that combo. A good intake sized for that size engine would be a plus too.