Hello Malcolm,
In answer to your initial post, unless you specifically want to use brass or bronze balls, you can use ordinary steel balls which of course are much more in keeping with an original engine. These can be softened by heat treating and allowed to cool slowly – preferably as slowly as possible. I used hot sand gradually turning the heat down over about an hour. The ball can then be drilled using an ordinary HSS drill bit.
You can also purchase 'soft state' single balls from here Simply Bearings who have them in 9/16 diameter.
I have placed some photos in an album of the hardened balls being treated and drilled for the governor for a Waller Engine which may be of use/interest to you.
Hope that helps some, if you have any further questions I'll be glad to try to answer
Regards – Ramon
Edited By Ramon Wilson on 21/06/2020 22:54:49