the -4 designation is per 16th. an -8AN would be 1/2 (or 8/16) a -4AN will be 1/4 (4/16). check the thread depth or just go get the right fitting. Personally, I wouldn't use the npt, I'd make sure I got the correct AN fitting especially for fuel in the engine bay. Summit can have it to you by Tues if you order it tomorrow.

*EDIT*
or try some of your local hydraulic stores. I searched for hydraulic in yahoo in springville, ut. There's tons of places near you. Call them up.