Simple Linear Encoder?

I'm building a hydraulic press for hot metal work. It will be
outfitted with a 12 V solenoid valve to allow an automatic mode
where the ram repeatedly engages the metal and returns.

Since the ram speed is fixed, I plan to set the speed of the
repetition by adjusting the length of the return stroke. I'd like
to be as accurate as I can in setting the depth that the ram
advances into the hot metal before it returns.

Others have done this with a set of limit switches, but before I did
that I thought I'd have a look for alternate options. One thought I
had was a small (cheap) surplus servo motor with an encoder, fitted
with a spur gear that would run on a rack. I don't know what would
be required for reading the location and turning it into a signal,
though.

Any suggestions or information is appreciated.

Ed