From what I can tell "Hatcher's Notebook" was written in 1947 (original publishing date). For some of the same reasons that I wouldn't utilize reloading data from 1947, I would shy away from antiquated gunsmithing information. It obviously has revisions to the book (up to 2008 that I found), which means that more current information has probably been added, but the point I would make is that he can BUY a NEW gun with that caliber, cheaper that doing a conversion. It's that simple. The labor and parts costs will easily exceed buying a new gun in that caliber, or buying a new gun and paying for the conversion. That's in addition to having a rifle that can actually handle the pressure of a wildcat cartridge chambering.
From the late forties until about the early eighties, it was cost-effective to "sporterize" rifles. That's why it was popular. Military surplus rifles were cheap and plentiful. Economical sporting rifles were not. The trend was to convert many different rifles to "sporting" applications. Chambers were converted to "sporting" calibers and wildcat cartridges were tinkered with. The times, they have a-changed my friend. We now have very economical "sporting rifles" in a broad offering of calibers. With enough looking around, your friend can find something already set up for what he wants. It will most likely already have all the things he'll want done with it (e.g. not having a 5-6lb. trigger pull). It will likely be lighter, stronger, and have better ergonomics as well. Most importantly, it will be safer.
Hope this helps!