Hi Ian,
Beautiful prep work and informative instructions here!
I did notice that you have 37-41 spindles I think with an after market "hairpin" steering arm. I had originally planned doing the same. I changed my mind after searching on "bump steer" and whether this arrangement could be a geometry error. I bought kingpins from Richard Lacy and talked to him about the steering arm. He highly suggested using the 32 spindle which I also had.
http://www.earlyv8garage.net/
I've put a few thread quotes below and a picture of my 32 stock spindle with 40 backing plates. As a minimum you will need a shorter drag link. Speedway sells them to a length you can specify.
Quote from Richard here:
https://www.jalopyjournal.com/forum/.../#post-8018947
"We highly recommend using the original spindles on 32-36's. It is especially important on 32-34's because the aftermarket steering arms are made incorrectly and always have been, which results in the original draglink being about 3/4" too long, which in turn causes the geometry to be incorrect AND when the steering gear is on high center, the vehicle will be making a left turn!!!"
Another thread with good explanations ,
https://www.fordbarn.com/forum/showthread.php?t=30373
"rb-- i don`t know of any steering arm that is made correctly today or in the last 70 years with the correct offset. it amazes me that manufacturers and hot rod shops don`t realize that the steering arms they are making and installing are made wrong. it would be so simple to make them right. obviously they don`t test their designs or installations. adjustable draglinks and clocking pitman arms will connect the steering box but it won`t correct the geometry and will turn more turns in one direction from center. the center cannot be changed because of the high spot in steering box. this makes it steer tighter in the straight ahead position. the only proper fix is to bend the after market steering arm forward the same amount that all stock 28-34 spindle arms come from the factory"
"RB, to expand on what Barry is saying the arm on the stock spindle is forward of the axle so that the intersection of the arm and the drag link form a 90* angle with the wheels pointed straight ahead. That is the geometry Barry spoke of that allows equal steering in both directions. As far as the stock arm raising when you turn left that's happening because of the caster setting on the axle.
I don't really know about the stock spring loaded d/l ends but I can say from experience that if a side steer d/l, with tie rod ends or even Heim joints, moves up and down on the same plane as the radius rods (wishbone, split 'bone, four bar) the bump steer is negligible"
Glenn