The bending tool I use is simply a piece of 1 1/4" galvanized pipe connected to an inexpensive heat gun. The right angle elbow on the end of the pipe helps restrict the airflow but also helps warm your toes on chilly days. The heat gun allows different heat and airflow settings so you can control the temperature of the bending pipe to suit the wood you are using.
I spray the rough lute rib with water and free-form bend the rib by hand enough so it can be held in the rib form as shown. It's easy to provide downward pressure on the form based on how the rib is "giving" to the heat. Rocking the form slowly back and forth assures that the rib will eventually assume the profile of the form.
Once the rib is close to final profile as seen below, I use the form to mark in pencil the rib outline and remove all the extra wood using the band saw. Then, repeat the wetting and bending process again with the rib close to its final shape. Since a lot of wood has been removed, it's now easier to bend the rib accurately to its profile.
After the rib is bent, clamp it back in the form and trim the edges to smoothly match the form. Here I have shown a monster spokeshave being used for the smoothing operation (I find it easy to use), but I'm sure any really sharp tool would work. The caution here is to watch the grain carefully and plane accordingly - or you can get splitting - necessitating appropriate language for the degree of splitting....
As the last step, I lightly hand sand each rib on a flat board with various grits of sandpaper glued to the board.
Go here to see how to assemble the ribs without using a mold.