I would practice cutting both pieces first. While your handsaw miter box may be fabulous, I find a I can get a much smoother cut with my Hitatchi compound miter saw than I can with the sharpest handsaw. Just my experience. Be sure you cut orthogonal to the centerline of the stock, otherwise you are going to induce some cast.

_________
BrentD, (Professor - just for Stan)

[Linked Image from i.imgur.com]