As someone who has (and had) Escort 2Lts with standard 32/36DGAV, 38/38DGMS, Twin 40DHLA and Twin 45DCOE, I can tell you the difference... As you go up that carby range, your fuel economy drops and tuning issue get more complex, but power rises (assuming it is all dyned correctly as most twin setups are not done well...)
For a good all round road car with the odd bit of competition occasionally, I would suggest the 38/38DGAS. You will notice a minor increase in fuel consumption, but also a good increase in mid range torque and power, and combined with a compression rise and extractors, you should see 15-20ish % (I think 30% is a little optimistic...). I can get 35mpg with all the above carby setups on a long fwy cruise, but if you more than tickle the throttle on either of the twin setups (which you do do...) then mpg drops rather quickly, especially with twin 45's... Also for twins you really need a cam to get the most out of them... But that is a different story altogether...

Yep they're emissions alright.
they were originally factory fitted on some 2L alfas so will work on an escort fine, especially if your escort is pretty standard. the trouble will be if you start modifying, then the carbs wont be very tunable. here is some quick reading for you. http://2108.lviv.ua/archives/dellorto-dhla-40-universal-performance-112.html
 
an emission carbs works differently to a standard DHLA or DCOE carb and cant be tuned the same.
the thing with emissions carbs is that you don't want to go changing emulsion tubes. emissions carbs are designed with specific emulsion tubes and they don't take kindly to being changed but they work well as standard and will give good economy.
I had DHLA 40G dellortos on my car for a while, although not very long. these are emissions carbs and I ran them on a pretty modified pinto. it ran super lean most of the time and I ended up with 70 idle jets just to get the mixtures somewhere close.
you should probably start by looking at the jets that you have in there, and then a rolling road session is invaluable to look at mixtures and where you can cut down a bit if you are looking to improve economy.
the standard jets for a 2L alfa that these come factory on are 32mm choke 150 or148mains 55 or 58idles, 210 air correctors and 40pumps, depending on the model.
 
good luck.