That's all for now,
In the video, Robert O'Brien explains the best procedure for using the router to cut away the shoulders of the heel block leaving a dovetail tenon that should fit nicely into the mortise already created. Robbie recommends, and I agree, that the last 5-10% of the shaping of the tenon should be done by hand. Once the neck is fitted to the guitar, the center line can be checked by pulling a black thread down the center joint of the top to the center of the neck at the nut. Slight adjustments might need to be made by hand. This is not uncommon in a home-shop set up.
THE DOVETAIL TENON
Cutting the dovetail tenon will set the angles at which the neck joins the body both left and right and up and down, i.e. both of the critical variables. Proceed carefully and check your work often when cutting the tenon.
When the neck is placed in the tenon jig correctly it should be exactly square (left and right) to the top of the jig (i.e. the travel surface of the router). To keep the dovetail tenon square to surface of the fixture and on the center line of the neck monitor the set up through the observation hole in the jig. Woody plugs a short length of spruce with the centerlin marked on it into the truss-rod channel. By eye, I line up this line with a mark I've made at the bottom, center of the viewing hole in the fixture. This is just a little aid in making sure that the truss-rod channel is aligned correctly.
All of this assumes that you LMI Neck Angle Jig has been assembled correctly and to tight tolerances.