I usually take a 60 degree file (3 Sided). I grind the surface off from one side to make a safe side. Then I clamp the part in a small vice with the bottom up extending about .040 above the jaws of the vice. I place the safe side of the of the file down against the top of the vice and file the angle into each side of the part. File a little, measure a lot. Adjust the exact height you need; .040, .030 or what ever depth your mortice is. When you get the height right adjust the width and taper if you wish to make a taper fit. And you are done.
