Um, Cosworths were fuel injected. Once that is gone, I think you can add anything you want. There is a Cosworth Vega site out there on the web. They will probably have a better answer than mine.
The only Vega's that only had a little rust were the ones still on the assembly line.
There was an aftermarket kit available for the Cosworth for a pair of Weber carbs, but they are few and far between. Once in a while you will find one on eBay, but be prepared to get your wallet out. They don't come cheap.