I measure from the frame rails near the front where it starts to bend inward. It's hard to get a constant height because people have different tires. I think CharlesH was at 10.25" with his stock LT's. After we adjusted his torsion bars he was at 11" (hopefully Charles will remember).
There is also a Nissan measurement that goes from the center of the A-arm pivot bolt to the front sway bar bushing, but I don't remember the distance offhand.