For installation of the STBA bushings, all you would have to do is accurately drill the existing .154 holes on the same center point using the #1 drill bit.  Its important to make sure that you don't wobble or similar and make the holes oversize.  Then with a hand tap and some tap oil, use the 1/4-40 tap to carefully hand tap the holes. 

 Next you will want to thoroughly clean the holes with acetone or similar to remove all oil and residue.  Then blow dry and apply some red locktite and using the installation tool or allen wrench as appropriate, screw the bushing into the threaded holes being very careful not to cross thread them.  We don't have a torque spec other than tight but not to the point that you damage the threads, the bushing or the tool.

Allow the locktite to set before use.  When you install the hammer and trigger pins, they may be tight in the bushings and that's good.  However, you have to ensure that the pin will allow the hammer to freely rotate.  You can do this by putting the pin through the hammer before you install both in the receiver and make sure the hammer rotates freely.  If the hammer binds on the pin, something has to give and as a fail safe, the right bushing will unscrew from the receiver.  Under normal use with a correctly sized and lubricated hammer, it will work as intended and not be an issue.  The pins are captured in the receiver by the spring identically to a GI lower set.