I tapped the manifold today. I had to go to home depot and get a 1/4 npt tap. They recommended using a 21/64 drill bit which is near impossible to find in any store so I used a 5/16 and then opened it up a tad with my dremel. The tap worked great, I tapped it a little bit at a time since the pipe thread is tapered. I got it to sit at the perfect depth and it gets nice and snug...
I learned my lesson the first time I used a pipe thread tap. I ran the tap in too far and the trans plug I installed never got tight and just screw in all the way through the trans case...
anyway here's a pic...
