Fuel Swapping From 2bbl To 4bbl

Well it is streight forward but, I dont think you can put a 4 on a 2 manifold unless for some resone its designed to be adapted for eather.
Can you post some pictures

I agree with Big Blue, it's possible it has an integrated, removable adapter. If it doesn't, I use one of these guys:

http://www.summitracing.com/parts/mrg-1933?seid=srese1&gclid=CJf13Y3d78YCFZKRHwodkKMJwg

This will let you put a 2-bbl on a 4-bbl intake, or the other way around too. I'm actually running this on my v6 turbo since the only available 4 barrel manifold is expensive and hard to come by, and I needed a bit more fuel. I've had no issues with it. I imagine the flow isn't nearly as optimal as a made-for-4bbl manifold, but it runs and idles well.

In my experience an out of the box Holley is going to be tuned fairly well for a stock small block. A little idle mixture adjustment with a vacuum gauge, and set the idle speed, and it should run pretty good if not close to perfect. If you have a radical cam or other major mods then it'll take a bit more work. Definitely check the float adjustment though, they often don't get that quite right out of the factory.