1972 360 engine fuel pump/ carburetor issues?

Hello!
I recently purchased a 1972 b300 van with a 360 5.9 engine. The van has been having a rough time. The previous owner had installed a small electric fuel pump that bipases the mechanical one... I'm not sure why... So I started installing the new mechanical fuel pump when I notices that the double barrel carburetor is only pumping fuel from one of the barrels...

Could this be the reason why the van is having a hard time running/starting?

Would cleaning the carburetor fix the problem?

More info on the van- it hasn't been driven since 1999. Only has 66000 miles on it. Despite fuel issue was able to drive 3 hours home.

Any info or advice on the 360 is much appreciated. It's a bit harder to find info on the 360 than the 318....

Thank you!!!
Author: Ryngus