I have retro-fitted the electronics with a both a PC based design using a 1 or 2 axis Galil card, and a stand alone system using a maple OIT.
Of course you dont need G-code programming for a break or a shear, For the mechanics you could reverse engineer from a present system, they all use a little bit of a different method, the obsolete DynaBend used a rolling ring drive with a linear scale instead of a ball screw with an ecoder on the motor which is the more common method.
For the height gauge it is usually done with a linear scale and interrupts the hydraulic valve when at the programmed height. On the PC based systems I used a 10.1" LCD screen to keep it compact, with the PC in the Pendant.
A typical commercial price on just a back gauge with no height control is around $14,000