I have a better trick, and it is free!
The only real difference between 1/8" npt and 1/8" bpt is the outer diameter. Take a 1/8 npt die and run it as far onto the auto meter senders' threads as you can. After you do this the sender will thread right into the stock hole in the block and seal perfect without even needing teflon tape. I just did it on the Cressida motor we just built with the Auto Meter Sport Comp electric oil pressure sender. Now as for you not reading any oil pressure, that is weird. The gauge hook up was so easy with ignition, ground, and the input from the sender. What resistance are you reading from the terminal on the sender to ground? I think it was around 250 ohms and it drops to about 125 ohms if you have the gauge hooked up because the gauge has some internal resistance.