Its fairly easy to do the 1/8" NPT mod. The problem most people run into is that they tap too deep meaning that the fitting will be threaded to far into valve area. The fitting then binds the valve spring up. To correct this mistake most people will solder the fitting in place. The reason is they have to back the fitting out enough so that it wont bind but it then leaks.
To do this correctly you will have to buy a "shallow" tap that wont thread to deep. You can do it with a regular tap but from the sounds of it I wont recommend you try. Pipe threads are alot different than standard threading and most people dont get the compression/tapered concept.
There are many different ways to go about this and if you feel unconfortable doing this PM me.
"I wish simply to be a decent person, yet I will always fear the retards" -Brian Hindt(geech) MCB Moderator Kidney Machine