Paul,
i just went thru this on my MGB and I finally decided to go to the tire shop I've used for 20 years even tho they were hesitant to mount/balance them. I took the sheet showing the correct way to do it and they did multiple mountings to get a correct fit using just the wheel. They sent someone to their warehouse to find the old mounting cones and must have spent a couple of hours on this project. The result? 6 wheels mounted with new tubes, balanced with a minimum of weight, not a single scratch, all for less than $100. I think most of the old time tire shops have the ability and equipment and if you give them the proper way to do it and they actually care you can get good results.
Rut