That's 1/4" NPT on the pump in Your original post, ....NOT the passage....LOL!!!(directed at 1st response)
You can get a fitting for a 3/8" steel line with 1/4" male NPT no problem. I've gotten some fittings that were smaller than the tube ID(5/16"+), I just drilled & honed 'em up, but 3/8" line will deliver what You need if the system is done correctly no problem.
E85 does require pushing the flow close, the outlet isn't the challenge tho', yeah inlet will need to be free of restriction...a pusher pump or just going to electric is the best policy...I understand, I've lived with the whining-growling etc., it can be annoying..
I vowed to mount the next one in a foam-lined cage with some ventilation slots & EFI hose connections..