IMO this is not a good idea. You need a softener piston and possibly the seal and spacers for it. The right injector and throat, probably a new resin type distributor tube, resin, gravel underbed, salt tank, brine pickup tube w/air check etc. etc. but, you are going to end up with a time clock day timer unless you have a metered filter.
You would be better off buying a new softener with a softener version or a softener with a Clack WS-1.