340 with 302 cast head for pickup

Your going to have issues unless you have a tall block where the pistons stay below deck or you run a thick head gasket. The "10.5:1" pistons, if the deck is spec should be .018-.02" out of the hole. 750 Double Pump is far to large for the application as those small ports and that small of cam will give out long before you can use that much carb. What trans and gears?

If it were me, I'd either go back to a 318 and use the heads, intake and a 600cfm carb or find some 360 heads a 600cfm carb and your intake.