I have dual carbs on my 73 T4 engine.  I had it smogged to see how close to legal it was.  It was only about 100 parts above limit and I had no CAT installed.

The dual carbs, setup correctly with a working CAT might be able to made to pass.

Install:
Bosch Quad tip plugs
New cap/ rotor
change the oil
Wires, if not real old.
Change to electronic ignition- Drop in points eliminator- @$50-$70

Tune the Carbs.  Balance and adjust the idle mixture to as lean as possible without overheating the engine
open the air by pass on each carb to futher lean it out.
Possible smaller idle jet- only @ $3 each, four needed If dual throat.

Go smaller main jet to match venturi size.

fix vacuum leaks if any

install a working CAT.

Make sure valves have .006 clearence to avoid the lifter preload issure with VW lifters.

I could not pass emmissions and when I set the valves to -NO preload it dropped over 200 points in the HC measurement

DO this BEFORE changing carbs, a single will rob you of power AND mileage, I know I had one on my 73 custom 2L and power was bad.

Robert