Those heads can't support 400hp UNLESS you take the time to port them out- then they're pretty decent. That cam looks little big for your intended use, but it will run fine, just not have as much low end as I would prefer.
My only suggestion is to port the heads. I don't believe 305ho heads had steam holes so you wouldn't need a gasket for them unless you had them drilled- which would also be a smart move.
Summit has a budget line of carbs that came out recently- I believe they have a 750 for like $250, it would be plenty for that.
LASTLY, measure your piston dish volume, your chamber volume, and set your quench distance to about .040"- you can use that to figure your compression. No more than 10:1- preferabley around 9.5:1 for a daily driven truck.