Autometer part #3280 is the adapter that you need. The fuel rail is 1/16 NPT, according to the searching I did yesterday (on Stangnet). It was also said that local hardware stores don't have this sized fitting, so save the time and just order the autometer adapter.
I don't know what kind of quality the JEGS gauge is, but an autometer 2173 sells for about $30.00 from Summit (part# ATM-2173). The adapter is about $8.00 (ATM-3280).
If you do get the part number from NAPA ... can you please post the part #?? Is it OK to leave the gauge on the rail permanently? It mounts right a the Schrader (SP?) valve, right? Thanks!
yeah, i'll post the napa part # if they have it. i will be mounting the gauge on the schrader valve. i don't think there's any reason not to leave it on permanently...