I have played with shimming the steering box itself rearward. Take a U shaped shim ( body/front end shops have them or you might try the "HELP" section at Advance Auto) , loosen the bolts holding the box to the frame and slide a shim down over each bolt. Easy way to pick up a 1/16"- 1/8" ( + or -).

I even played with shimming just the bolt closest to the header. I did not notice any ill effects.

If you loosen the driver side motor mount ( the LONG bolt) and lift the motor by putting a block on the oil pan, you can slide a 1/16" piece of sheet metal between the frame mount and the motor mount. this will lift the header tube up slightly. These tricks may add up to what you need.