Tony, best sort out the "tad of play" first, have you tried adjusting it? If it has no more adjustment left or it is badly worn 'straight ahead' as is typical, then consider a rebuild by eg
http://www.geeltd.co.uk/gee/Fitting a rack & pinion means quite a bit of expense, Jack Knight is the manufacturer and can buy direct (maybe) or from Morgan/Dealer - it has to be a centre output rack of course.
Advice is really, sort out the box before considering major work to fit a rack - IMHO - PJB.
