I made something like this out of 3/8 for a guy but it was not made of tool steel. I don't have any way to anneal the tool steel then harden it back. I would be afraid of warping something that long and small diameter. Otherwise I could help you out.
Shorter sections would fit in my oven. I am limited to 14X14X8 but I still think it would warp some. Being that you need smaller sections and it's not being used for high speed rotation a few thou maybe acceptable to you. I have some O1 rod that size. I might play around with it this weekend and see how it turns out with a 10" or so section.
Not sure what you mean by "single point". Do you mean ask/purchase each one as needed. As far as wear. II am just reacting to what was said on a video of the planes by the new owner of Union Mfg Co. He commented that he tended to see a lot of wear in the vertical post threads with the old X Unions that he has seen over the years. The arm that is lifted and dropped by adjusting the nuts is extending and retracting the iron/blade. If the screw cap is tight it could take a fair amount of force to move. Logically one should loosen the screw but... my planes that I refurb are going to others. I am not a machinist so I can't really argue whether the rod needs to be harder than mild steel...
