I made some jaw faces for a small Wilton Flip/Grip vise that I restored 3 years ago. I wanted it to have the capability to hold small rod stock at both vertical and horizontal positions. After machining the faces and fitting them to the vise (using a Bridgeport type mill), I clamped the jaw faces end to end in the vise, set the head at 45 degrees, and cut the "horizontal" groove in both jaw faces a quarter way down from the top. Then I positioned the jaw faces top to bottom in the vise and cut the "vertical" groove in the center of the jaw faces. Positioning the jaw faces in the ways that I described above allows me to keep the cuts perfect by making one cut for both pieces. Remember, you are machining these faces as mirror images of each other (don't ask me why I stated that reminder).
One other thing to consider is that the Wilton vise that I mentioned was light duty enough that hardening the jaw faces wasn't nessessary. However, you may want to look into that, even if you do the crude hardening method of heating the metal to cherry red and quenching it in a bucket of old motor oil.
Good luck and please post pictures of your speed vise and your jaw face build. I restore vises of all types.
Good Luck!
