Re: adding a carb?
No, it is not possible to add a carb and in reality, even if you custom made a manifold, you would not get much increased performance. In fact, you just may over-carb the engine and get really poor performance.
I modified a 55 Chrysler to accept a bigger carb and the engine simply would not run well with the added venturi area. It was over-carbed. You can search some of my posts about it on the Force/Chrysler forum. Search for "Say hallo to my leetle frand."
Don't bother wasting your time trying to add a second carb.