I can't help on the rack availability , it is just not a spare that is in my cache.
The only advice I can give is about the ratio. If you want to drive the car on the track at all, then the quicker the steering ratio the better, my old +4 had the long drop arm from the steering box which gave about 2.7 turns lock to lock. Yes it will be heavier at parking speeds (but nothing like as heavy as the old cars were before the advent of steering bearings and r & p) BUT so much better once moving. Therefore I would recommend going down the Wolf Performance route with Cain.
