Sorry, I'm a bit late to the party, so the following will be partially redundant after Carlo mentioned it already. One thing that the crane folks use, especially on the really heave ones, is called a derrick boom.
https://www.google.com/search?q=derrick+crane&tbm=isch
This would be a simple way to handle the forces, while keeping bending moments in the rail low.
For the purpose of erecting the launch pad, you could use a variant where the rope is not fixed to the derrick, but only gets redirected by it, so that the rope gets "released" after the pad has been erected by a certain amount. Imagine a derrick boom with a structure looking like a two pronged fork on its end to guide the rope as long as necessary. The following graph hopefully illustrates the idea:
View attachment 175852
Assuming the rope is more or less horizontal between the derrick and the winch and that the CG is at the location where the rope is connected, the maximum force in the rope calculates to "force_rope = weight_cg * (length_load_boom / length_derrick_boom)", so if the derrick boom has a length of 5' we end up with about 361lbf. This is also about the force that the pad anchoring has to resist, to prevent dragging it over the playa. Under the same assumptions, the force in the fulcrum is in the neighborhood of "sqrt(weight_cg^2 + force_rope^2)", in this case around 418lbf. In real life, this force will be slightly higher because the rope will not be exactly horizontal and the winch will also pull it down. However, this is a reasonably good approximation for our purposes (unless you plan to build a fulcrum that fails at exactly 425.000lbf :wink
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Other forces: the axial force in the load boom will be "sqrt(force_rope^2 - weight_cg^2)" (about 294lbf) and in the derrick about 210lbf (the weight at CG).
Most of the involved forces can be reduced by making the derrick longer, but at a certain length it becomes inconvenient to handle. In theory, one could also have multiple ropes that get connected to different points of the rail with the forces distributed by some kind of pulley mechanism (see
here if you're really bored). However, if this is necessary, this would probably be a sign that the rail is not strong enough.
One detail, that might be relevant: Where are the support points of the rocket on the rail (rail buttons and, if present, temporary support during erection)?
Reinhard