On the contrary, the NA pump will flow the same amount of fuel as the TD pump. It also can achieve the same economy or power if all you changed was the pump from 1.6TD to 1.6 NA.
However, part throttle without the LDA/AFC, it is allowed to have full fuel with little throttle adjustments.
The 400hp 12v referred to also has a AFC setup, so when there is No/Little boost, little fuel is used. This helps fine tune the fuel at part throttle/part load, unlike a NA pump.
Add some more timing and any diesel will run a bit better mileage wise on the same fuel. The US emissions suck period. Just a timing bump on mine netted .1 tenth faster 1/4 mile and a 1mpg average increase for mixed driving. Highway it added 1.5-2mpg.
You still have yet to convince me the turbo is helpful on an engine built for NA. By the time he builds it right, he could have used said money to buy more than a handful of full fuel tanks. It is like the guys that swap a Duramax into a Suburban for "mileage", it will never add up.
If he wants a fun car with a minor hit in mileage, then by all means turbo it. Ultimate economy, keep it as is.