Ash,
Hey there. Bob Janes at Coorparoo did a wheel balance for me on an old 504 wagon a few years back now.(was done with wheels ON car.) Give them a try, if they can't do it they may offer some guidence.
Also a couple of years back now I remember seeing an article in a "Rallye" about crude home balancing of older style rims.
Chris
Ken Graham at Accurate Suspension at Woodridge can do them. The jig for them is probably still set up from me a few months ago. It seems only froggies did not put centres in their wheels. His no. is 38082878