The truth about 130mm OLD into a 126mm rear dropout frame is sometimes you can shove it in there with no issues, sometimes the dropouts flare. When cold setting a steel frame the same holds true.

When using 2x4’s, threaded rod, bottle jack, or whatever, the frame has to flex beyond how it was produced. There are no absolute guarantees that every frame will flex consistently on the DS and NDS. It is generally a backyard/blacksmith process with no jig but generally works fine.

John