Using a plumb bob, I tape-marked reference points on the floor showing the tire's centerline, then measured the distance from the tire's center to the airplane's center (previously plumbed and snap-lined). I then measured and marked another point about 10 feet aft from the tire, showing the same distance from airplane center to tire center. I snapped a line showing this reference line.
Now, with the billboard reference centered on this snapline, I stuck the wheel pant aft end hole onto the 8 5/8" pin, then centered the wheel pant front end on the tire. I centered the pant's centerline mark on the tire's center tread, then clamped it all into place.