Reaming

 This is the basic setup for reaming legs.  Your looking at the bottom of the seat, and the sightlines have been transferred to the bottom.  The leg holes have been drilled ( 5/8), and I have the square, bevel gauge and reamer ( 6 degree) is in the hole.  The reamer works like a charm.  It is a turned piece of hickory with a slot cut in it, and in that slot is a piece of steel sharpened like a scraper.   One big advantage is that the scraper cuts from both sides, so it always stays centered in the cut.   I got mine from Elia Bizzari at handtoolwoodworking.com.  He sells these reamers and the matching tapered rounders, which also work great.  By using both tools, you get a perfect mating when the leg is inserted.  There are several reasons for tapered tenons.  Once you get comfortable with the reaming, you can fine tune the legs, stumps for perfect alignment.  It also makes assembly easier, and when you insert the leg, the glue doesn't get squeezed out.  Then you split the end of the leg and insert the wedge, and that leg will never come loose.  Add some stretchers, and you have an undercarriage that will last generations.  But more on the reaming.

 Here's the look down the gun barrel.  The square is aligned with the sight line, perpendicular to it, and the tip of the reamer is then aligned with the square.   The easiest way is to line up the square with the sight line, then find the tip and ream until it lines up.  As for the tilt out, lay the bevel gauge on the side of the reamer  (remember to set the gauge to three degrees less than the desired angle, half of six) and ream to keep the angle correct.  Its easier to do than I've indicated here... practice on some scrap until you become comfortable.  A couple other things.  I used to shape the seat and then ream, but now I ream while the seat is flat.  After reaming and adjusting, I then saddle the seat.  Its really easier, and I've never had problems tearout around the holes.   The other tool is the bevel boss angle finder.  I first used it on boats, before I started chairs, and it allows you to set the angle quickly and accurately.

This is a shot of a dummy leg, simply a 1 1/4 strait turning that has been reamed on the end.  I have a couple of notches turned into it.  As I ream, I test the reaming depth with the dummy leg,  and once the end peaks out, I set a second bevel gauge to the height of the notch, and use this second gauge to make sure the four legs are reamed to the same depth. 
I've tried other methods, and this is by far the easiest and most accarate.  Now I just have to find a buyer for my old reamer.