a few answers
1: There are many power steering options. I take it you don't plan on having the original motor right? For instance; if you have a 350 engine, you could find an early '80's chevy truck and completely use the power steering unit. Including the box and pump. The arm that runs from the box to the main steering rod may be a different length, but if all else fails, you can fabricate one.
2: To lower the rear you'll need shorter springs. You can use lowering springs that they offer for the 63-66 trucks, but you have to notch the main frame. And Chevy duty sells a C-notch kit for the 60-61 trucks.(I've seen this set up ran before)
3: As far as doors go, look around at junk yards, you'll be surprised what you can find. As far as fenders and a hood, you have the option of fiberglass or steel. Chevy duty offers the fenders in both styles, but the hood in fiberglass only, which is a 63-66 style. I imagine you have the type of hood with the two large oval ports. If you are looking for a hood with the two oval ports, I happen to have one in reallly good condition for sale,($300 + shipping).
I hope this info helps, let me know about the hood.
-superman.