55-59 front axle centerline?

[rcs72]

I'm getting ready to install a Scott's IFS (1st attempt at IFS) on my 59. Shouldn't the axle centerline be a known measurement?

For example;

1) Heidt's & TCI say to measure 20-7/8" from the front shackle bolt centerline.

2.) Jim Meyer Racing say to measure 26-7/8" from front of frame.

3.) Scott's say to get the centerline from the stock king pins. This doesn't make sense to me because there is no weight on the suspension. With weight the axle would move forward and w/o weight the axle will move back.

4.) No Limit says the centerline is the 1/2" hole on top of the frame. They also recomend moving it forward 3/8" to center the wheel in the opening.

Thanks