2002 Express Van 5.7 Dual Exhaust to Single Exhaust.

[Fast355]

Not completely sure what you want to do or asking but dual vs single cat systems only differ with the after cat sensor or sensors that monitor cat/cats efficiency. Neither have anything to do with engine operation. Both would still use 2 pre cat sensors. You could just disable the after cat/cats O2s and it would be fine. You just wouldn't have any catalyst monitoring should a cat go bad.

Incorrect, 3 upstreams on the factory single cat trucks. It very much does change how the engine runs.

GM has factory Express van tunes for L31s with a single cat as well as no cats and even no 02s at all. Some of the L31 calibrations are open loop only even.

Tunercats has the option to directly edit the Dual vs Single cat exhaust configuration, I made a dual cat 305 calibration when I put the L30 into my Tahoe and also made a single cat L31 calibration when I put a Mercruiser version of the HT383E into a 2005 Astro.