Might be iffy? That is the definition of iffy. They make 26.8 seat posts, they are not super hard to get. You can find vintage versions, modern Thomson versions, Nitto makes a nice one that has a classic vibe or you can go cheap and go with Sunlite, Dimension, Kalloy or one of the other many low cost seatpost options.
There might be other options as well that I don't remember because I bought a Nitto 26.8 and don't need another.

I laugh when people spend so much time and effort to do something that already exists in a better safer option. Though I guess if you have a lathe you might as well have fun with it.