So I'm in the 3rd whole from the front with these 52s and Kirt's mounts. I'm also using some 6" shackles. Leaving the frame eye mount in the stock position.
These ORD 52s have a center pin 24.5" from the front eye. (I bought these new but 2nd hand, think they were ordered that way) With this set up, the axle is 1/2" forward from stock. I also measured 52" straight across and checked that my shackles wont bottom out on the body mount, they come close but do not. So I hope my shackle angle is optimal for all three.... stuff/ droop/ and ride. Since the axle is 1/2" forward from stock, this means it's about 1" REARWARD from where I had it previously. I don't think you can see by the pictures, but my tire wear on the inner fenders with 37s was perfect. Tiny bit in front, tiny bit on firewall. Sooooo where it currently is wont work.
So I picked up some new hardware and allen center pins for my zero rates. I will once again be using them to move the axle forward 1.5". This will net me a total of 1/2" more forward than my previous set up. With the new 40s coming, I can always trim off the front of the wheel wells but not the firewall.
My concern right now is, I can move the spring bolt forward another hole and get about the same movement forward on the axle. This would also make my shackle angle steeper. I'm not sure at this point which is better. It would be nice to have the U-bolts centered over the axle instead of offset, but I've also ran it this way for years so why should I be worried LOL.
Of course this shackle angle is with the springs laying on the axle, no weight.