Kay - I'll try explaining this another way
Looking at the jeep from the front, x being the horizontal axis, and y being the vertical. Given that the spring flexes in the y axis, and is remarkably rigid and strong in the x. Also given that the axle, the 2 springs and the perches (rear end of the spring) form a remarkably rigid and strong square. The front of the spring can not move in either direction of the x axis without another component failing ( that being, a spring bending/breaking on the y axis which is virtually impossible except at the eye, or a rear perch tearing off, or a rear eye bolt shearing, or theoretically - axle u bolts breaking) - the x axis locating of the front of the spring is not secured by the shackle, it is located by the rear perches and the rigidity of the square structure and the rigid strength of the springs in the x axis.
Consider the "C" shackle design, still used today in hd and military applications and previously on willys jeeps. Why don't the springs slide off the "C" because of the structural principles I described above. Most have nothing in the way of a clip or pin holding the spring eye on the "C" because the structural design does the job just fine.
Given the jeep in the ad has H-braced shackles, even at that length, and assuming mild steel material it would still take major force for them to collapse and you would also see either a broken or severely bent spring(s) or a sheared rear spring eye bolt or a ripped off perch.
They few times I have seen a shackle failure it was accompanied by substantial damage to one or more of the other components. And in every case it was taking epic air and significant force applied to generate the failure.
Although the shackles look really weak, and certainly are the weak link in that set-up they are not as weak as they appear - the shackles support the jeep in the y axis and do significantly less in terms of the x and from design perspective they allow the spring to lengthen and shorten while supporting the in the Y
Whether the builder knew it or not retaining the track bar also adds a good deal of strength to the x axis
Anyway hope that explains it...
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