A word of advice on the on the steering gear. Regardless of the mileage on the gear send it out to be rebuilt before you install it. You sure don't want to have to pull it back out after you get the interior installed (The gear column and all have to be removed thru the floor into the passenger compartment.

As far as a PS pump there are 2 easy options as far as pump and bracket. One is the older TRW pump....as I recall the pressure is listed as being a little higher than the original pump but it will be fine.

The other option is using the newer brackets and a Saginaw pump. The majority of Saginaw pumps are made for the integral steering gear and has considerably higher pressure than the early Mopar gear is designed for. The trick is to spec a pump for a 70s Corvette with the slave cylinder power steering. Those pumps operate at a lower pressure and should work well with the early Mopar gear.

A couple of other things come to mind if you're using the original front suspension. 57-8 Chrysler Windsor torsion bars will fit under the 57-58 Dodge and Plymouths and are a bit more HD that the stock bars. Factory front sway bars are kind of rare on 57-58 Dodge and Plymouths. If you come across one they were standard on the 57-8 Imperials and will fit the Dodges and Plymouths (I suspect sway bars from Chryslers of that era will also fit). You will need to either cut off the frame brackets or fabricate some (I can send you pictures of the ones I built for my 57 Plymouth if you need them).