Highest flowing sbm heads?

700hp on pump gas, like 93 octane at 416" will take decent ported W8's or 9's, ported intake, a Ritter or R block, a solid roller in the mid 270-280° @.050", 700"+ lift, decent rods and crank, good oil control, good machine work and assembly. And don't be scared to turn it up. This is how I'd do it, your mileage may vary.
In general I agree but it would be challenging nonetheless. And with a cam like that any kind of street manners are going to be out the door.