I went back and read your original post and one point you fully missed is that you have to have an AN fitting to fasten an AN fitting to. They don't connect to standard fittings without an adapter.
AN fittings were designed and still used in the aircraft industry. They got adapted to hot rod use much later. Now street car guys like them because they "look cool" but most of the time aren't needed for regular street rigs. A bit of history on them plus a good explanation here.
https://www.pegasusautoracing.com/do...ocID=TECH00096
NOW UPDATE after the coffee kicked in and I started looking at you photo of the pump the fitting you show is on the OUTLET side not the inlet side.
That normally is used with an inverted flair fitting and steel line running to the carb. The inlet is the tube that the short fuel hose that connects to the steel line running up the frame connects to.