Nathan:
I converted an old Nolan to butane some time ago. The orifice is much smaller for bottled gas due to its higher heating value. A 1/32" drill hole will get you into the ball-park, with some trimming of the pressure regulator and carburetor opening.
In order to change the orifice, you must disassemble the carburetor. Once the orifice is exposed you can determine the best approach: drilling-tapping-plugging-redrilling, or perhaps screwing on a brass cap and drilling the 1/32" through the end.
Now, it has been more than a dozen years since I experimented with this, but I distinctly recall having done the calculations, buying the off-shelf drillbit, and successfully making the conversion. Off chance it may have been a 1/16" hole but I doubt it.
Also, the stuff that you must use to purify lead is something called VITAFLUX, on internet auctions.
Say hello to your dad for me,
Dan Williams