if you use too big a carburator , you`ll not be using all the gas , it will go right thru...= waste...plus it wont run as good as it will with the 'right' carb... just for comparison...I had a 50 Holley on a 302 in my fiberglass car, got 14 mpg...got a smaller Holley , got 19 mpg and car was quicker!
Talk to Jon of Carbking , my suggestion, and get the right carb., free or not ,that free carb will cost you more in the long run!