Hi Peter, Im new to the site as of today but not new to these trucks. I have a 63 GMC 4x4 and heres what I used.
Several people have Emailed me about this P/S conversion, so I will list some part numbers. If you use the stock closed knuckle (1960-1969) Dana front end you must use these drag link parts with the 70-86 Power Steering Box. Latter steering boxes require different hose fittings.
NAPA 269-1105 Tie Rod End
NAPA 269-2441 Drag Link 1970-1986
ES2234R 1985 Blazer Tie Rod
The closed knuckle front end has a smaller taper and requires the Blazer Tie Rod.
I also recommend the quick ratio Steering Box. Several people make and offer these. One being, AGR Performance Steering, unit #292117 for $350. You can find a used GM P/S box for under $100.
You will have to space out the new box from the frame slightly and modify the end of the column for the longer steering box.
Jon.