Ea81 ports and intake manifolds are 35mm. You can fit a larger manifold but the ports in the heads will still be 35mm. There are also three sharp right angle bends inside the heads to kill flow. This is why the 32/36 doesn't have a higher top speed than the standard Hitachi.
As you know, the dgas is 2x38 and it's synchronous. It may feel like it has more power low down because it won't take much throttle opening to get full flow through the ports.
If you tune it right, you should get the same fuel economy at cruising speed, but you'll have to be very gentle on the throttle to get good economy around town.
Airflow through the venturis will be very low at low engine speed, which may cause poor fuel atomisation. This would cause a flat spot when you floor it unless you inject a good dose of fuel through the accelerator pump; another potential for poor stop/start economy.
Personally I think it's too much carb for 35mms ports, the 32/36 flows enough for at least 120hp.
I'm not going to say don't do it though. Nothing ventured, nothing gained etc. But if you find you get terrible economy around town, I'd suggest swapping the carb for a 32/36.