I have the correct air cleaner you need (yes they are different). Email me DIRECTLY (see below) if I can help.
I ordered a replacement. And had the same problem. However it was the carb that was the problem. The small bridge piece that the air cleaner housing screws into, was to tall. I replaced it with an original. Fit perfectly.
See, I learned something new today .................. I find it funny how Ford would have 2 bbl and 4 bbl carbs that could share the same air cleaner - but there was a different size for the 2 models of 1 bbl carbs used.
The RSB is 2 1/4"...the RSB air cleaner has a 2 7/16" opening. The '70-'72 RBS air cleaner is 14.62" diameter x 3.24" high whereas the YF is 13.47" x 3.63"...don't know the '73-'77 dimensions. Its a Ford Thing to keep people from taking parts off a red Ford and putting them on a blue Ford.