OK-
I'm the dude that brazes them up.
The plugs I use are short pieces of mild steel bar, machined to 9/16" diameter and the same length as the rocker post's width. Chamfer both ends 4 mm.
First off, you need oxy/acetylene, a butane/air torch is not hot enough for this job.
2nd, sit the rocker posts (pillars) on a brick an inch or so apart, heat them with the torch until all the oil has run out. The posts are not mild steel, they are either cast iron or sintered iron (using powder metallurgy), and both types soak oil up.
3rd, let them cool gently so they stay soft, do NOT quench them.
This also applies after you braze them- see below.
Brazing- I countersink both sides of the rocker shaft hole before welding the steel plugs in. I use nickel bronze 2.4mm uncoated rod, and bronze welding flux. The bronze flux cleans the metal better than the common `copper and brass' flux does.
You will need to get them up to a dull red heat for successful brazing. If you have not used oxy for welding/brazing, get somebody to do it for you.
<edited> typos, and more info added.
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