Carb sizing question

[boostin20]

I bought a 72 c10 last month and just put in a 350 with a RV cam. With the cam, it's only 20 or so horsepower over stock. A quadrajet 4bbl came on the old engine. I don't know what size it is, and I won't be around the truck to look until tomorrow. I put the old carb on the new engine and adjusted it at idle. When I open up 4 barrels (stomp the gas), the truck immediately falls on its face until I let off the pedal. My two questions are this:

1. What is the best size 4bbl carb for an engine with no more than 300hp?
2. What do I have to do (if you think I don't need a new carb) to resolve the falling on its face issue when the other 2 barrels open?