If the column and box are integral, then you may not be able to do it without changing the column. Have you talked to PlyDo or Butch's Rod Shop? What about the D15-P24 website?
GM used a "ram" style PS in the 50's that MIGHT be adaptable, but I bet it would be difficult at best.
I think there is a company out there that sells a kit to add PS to a stock 47-59 Chevy truck. I have never seen this kit, but it might be adaptable to your situation.