I am planning on lifting my '90 1/2 ton suburban either 4 or 6 inches some time soon. It has the 10 bolt straight axle in the front, and I am unsure of exactly what steering corection I need. Do I need a new steering arm or pitman arm? Maybe a new steering block or drag link? Please advise so I can do this lift right the first time.

I would just use a raised steering arm, for your application.

I just intalled a trailmaster 6" lift on my 85 chevy 3/4 4x4. I used a 4" steering arm and it worked fine. You will definitely have to get another steering arm. Mine came with my lift kit. Most places sell them for 50-60 bucks.