Welcome Martin.

First why retrofit is the old one bust.?

Secondly you need to detemine what type of motors and drives are being used. If servos then you need to identify if Analog or Step/Dir Drives are used.
Lots of older machines used Analog DC drives which limits your options slightly. If Dc Analog then might want consider doing full Retro fit and use AC servos with Step/Dir drives and Controller to bring into 21st Century.

I Only Fit Cslabs Controllers and they are Excellent controllers. However for full Industrial strength machine with simple needs, which this is, then I'd look to the east and Fit Industrial strength controller which doesn't require PC.

Most of the Cheap Higher end controllers will fit your needs but if was me I'd pay little more and go for Adtec or GK controller with better support.

However you'll need to identify if Analog drives first because most common Modern controllers are Step/Dir only. You'll need to Spec for Analog if intending to use existing Analog drives.