Yeah, the clock position references might not be the most accurate as it depends on whether you're referencing from the top, the bottom, or front or back.
I'm sure you're doing it correctly grizzly, since the arm on an EB will normally be pointed roughly towards the rear of the truck. But it can't hurt to make sure here.
I like to use "driver's side" as my reference. The pitman arm on a manual steering box should be pointed a few degrees towards the driver's side of the frame. Roughly 1-spline, or 10° generally.
Later models with power steering (after a certain year?) had the pitman arm pointed straight down the frame rail. At 12 or 6, depending on your point of reference.
What box is yours? (sorry, I forgot the manual in the title) What pitman arm? If an aftermarket arm, it could have been installed incorrectly by a PO, so it's always a good idea at this point to make sure the BOX itself is centered, and worry about the direction of the pitman arm secondary.
While the draglink is disconnected, turn the wheel back and forth to both extremes. Count the number of turns total, then bring it back exactly half way. Doesn't matter right now where your steering wheel is. It ONLY matters where the box is.
When you verify your box is centered, if the steering wheel is off-center then now's the time to pull it or the shaft yoke and re-center it so the wheel reflects the position of the box only. From then on, you can use the steering wheel position to indicate the tire's position. Not before.
Once you have the box on-center and the wheel straight, then you can see where your pitman arm is. If it's directly to the rear, you can move it over one spline if an aftermarket arm. If a stock arm, it's going to be where the keyed splines dictate. If an aftermarket and it's one spline off, you can probably leave it at that and be fine. Or you can choose to remove it and re-orient it to the proper angle without changing the box.
Then, last comes adjusting the draglink to fit.
Once you're driving it, if the steering wheel is slightly off, all that means is that your tires were not perfectly straight when you adjusted it, and can easily use the new adjustable draglink to re-center the steering wheel to the tires on the ground.
It's maybe more work this way, but from now on you'll always know for sure that your box was centered and the rest was matched to it. Not the other way around.
This is especially good to know if you are ever tracking down a wandering problem, or steering issue.
Paul