Tightening rear shackle nut on '49 Hudson sedan

[airbrushguy]

I am replacing the rear spring in my 49 Super, I have read in the manual about the c-shaped shackles and nuts.

I believe other cars like Chryslers used the same type of rear shackle:

 "Finish tightening the rear shackle nut.
It is important that the shackle be located properly so as to insure the bushing being threaded far enough on the shackle but not far enough to bottom the thread in the bushing as the shackle moves in its normal operation. Bottoming will cause a hard ride and shackle breakage."

Has anyone done this? Could someone tell me how to know when the shackle is threaded far enough? Should both sides be tightened the same amount? If not bottoming, then how much? Is there some way to gauge it?

[Jon37]

If you haven't done so already, I would suggest also posting this question at the Hudson Open Forum, https://forum.hetclub.org/

[airbrushguy]

Yes , I have posted it there. Response was that there could be a tool machined to help install it, since it was made from a 1/2” bar of steel, I would assume the shackle was left 1/2” away from frame and not bottomed out. 
But that is just an assumption on my part and all I can go by until someone with specific knowledge can help me.

Even RareParts who sold me the shackle didn’t know of a specific tool....