Power Steering Unit

Hello, I'm after a power steering unit for my defender. I was just wondering if it needs to be specific to the engine. It's a 3.5 V8, any help on this subject would be appreciated.

Power steering unit?
I presume you mean PAS Pump, the bit that bolts on the engine?
The other bit of the system is the PAS 'Box', that sits on the chassis rails; theres a couple of different variants, but most are the four-bolt PAS box and common to Rangies, Discos and Defenders.
PAS Pump, I cant remember, I think that too is generic, or at least to the box its attached to.... only fifference is the bracketry, whether its attached to a VM or TDI or V8, and there are a few variations depending on the actual variant of V8.
On motors with air-con, the pump is offset mnore towards the near-side wing to make room for the aircon compressor.
On earlier motors, I seem to recall the PAS pump is driven off the same belt as the water-pump and alternator, or off a short belt off a double pulley on the alternator?
Later motors have an 'idler' pulley with the aircon and pas pump driven off that.
So, what do you need, just the pump, or the pump and bracketry to attach to the motor?
And which motor do you have, is it an original factory fit 3.5 carb engine in the defender, or is it a Range Rover take-out dropped in substitution for a four-pot?

It's the original 3.5. Though I've just had a cage fitted and by pure luck and coincidence the company who installed it used to race a v8 and happened to have the parts required. so i hope to get those later this week and have them fitted in the not too distant future. Tanks for the help though, you clearly know a lot more about landrovers than i do!