For my project I got a power steering pump from a 2005 Volvo S40. Runs off 12v and has metric threads. FoMoCo part.
I'm using a vacuum pump from a Camaro ZL1 and keeping the stock brake master cylinder that came on my vehicle.
For brakes, you can add a vacuum pump (as Electric Land Cruiser did, and some production EVs had such as early Teslas), or you can replace the master cylinder with an electromechanically assisted unit such as a Bosch iBooster or similar units from other manufacturers (mostly used in hybrid and electric vehicles).
What you're building was very common for years, and is probably still found in many production vehicles, called electro-hydraulic power steering (EHPS) or electro-hydraulic power assisted steering (EHPAS). The unit from the Ford C1 chassis (which includes the Volvo S40 and my Mazda 3) is very common; the one from the second-generation Toyota MR2 was an early example and may be desirable because it works with no computer network communication. These were never specific to EVs; they have been used in regular engine-driven cars and hybrids, but most of them - and probably all EVs - have gone to direct electric motor assist on the rack or column instead.
I guess you would find one of those units on eBay or something?
... or an auto salvage yard.
That's why EHPAS exists: manufacturers introduced it to replace engine-driven power steering pumps, because the electrically driven version only runs as required, saving fuel - it doesn't run at full speed all of the time. Directly driving the rack or column with an electric motor takes even less energy, but the difference is small (which is why EHPAS is still a reasonable choice in production).
So it only uses energy when you turn the steering wheel? Useful.
It always uses a bit, but yes, it only uses substantial power when needed.
There are electro-hydraulic systems that use a normal hydraulic rack plus an electrically driven pump, and there are all-electric power assisted steering systems. The all-electric designs can act on the rack (not hydraulically), or on the column (both OEM and those aftermarket products).
Yes, the E85/E86 Z4 (but not the "M" version) had an all-electric system. The E85/E86 Z4 was mechanically related to the E46 3-Series, so the Z4's steering parts might bolt right into the 323i... it's worth checking out. This appears to be a system with the motor in the column, which makes sense because I know the 2014+ Mazda 3 is arranged that way (and you say that their steering systems were related); that means that you would need to change both the rack and the column, or use just the column (with motor) from the E85/E86 and keep the E46 rack but disable the hydraulic assist in it.
