[projectRDM]

I just did the same thing for a customer's car, used the 3/8" and grinded the flares down a little, then lubed the shit out of the hoses. It's janky, but the clamps hold it fine. If using OE hoses they're actually 8MM, so an aftrmarket piece of 5/16" fits a little better. I plan to replace it all next time I have the car on hand.
On my own car I have a Greddy sender so it's 1/8" BPST, I was able to piece it together with Earl's fittings, a 1/8" T then two 1/8" to a hose barb fittings, but those three alone were like $30.