I have a 2004 with the returnless fuel system.
I first started using E85 after I installed 80# Mototrons/changed IFR (injector flow rate) via HPT. (HPTuner)
At the time I had a stock pump with stock harness, and I ran that setup for a long long time with no AFR issues. (Live monitoring via wideband, fuel pressure, etc.)
I would recommend a Racetronix pump rewire, I've since installed one myself to help my factory pump as it reached higher mileage.
It can't hurt to change the fuel filter before making the fuel change, after one tank of E85, and again after ~5 more tanks.
If you have a smartphone, I would recommend looking into the app called "Flex-Fuel".
That app will display a GPS assisted map with all surrounding E85 distributing stations.
Good luck and enjoy the corn.
