Offy intake to 4100 carb adapter?

well after searching for several months now for a carb ( at a reasonable price ) to put on my sons Offy intake for his Duster, I found a 4100 Autolite carb that is 450 cfm that is used on small block Fords apparently these are a very good carb, the problem is the bolt pattern, the Offy intake is exactly 4" square on the bolt pattern and the 4100 is 5 1/4" x 5 3/4 ", I found an adapter from square bore to spread bore but it dosnt fit, dose anyone know if they make one?, I haven't bought the carb yet and don't want it if it wont work, thanks