Recommended 4bbl carb for stock 318
That’s good its already got the exhaust upgraded to a dual as it would be a waste opening up the intake end with a 4bbl and still having it choked up with a single exhaust.
As others have said, if you want to keep it simple yet get an increase in performance, get a 1406.
I upgraded mine two years ago and wish I did it a few years earlier!
LD4B installation on a 75 318