[Biturbos4] Steering rack differences

[Steve Schmidt]

I normally hang out in the urq world but could use some A4/S4 help please.
My son's project is an A4 to S4 conversion.
We stripped a donor car & I found that there are 2 different steering
racks......
The S4 donor car has a ZF & the older (97) A4 uses a Koyo rack.
Etka only shows different part numbers not ratios .
Is there any ratio difference ?
Since it would be easiest to change them now (without the engine in the car)
would there be any (other than obvioudly newer) advantage?
Thanks,
Steve Schmidt