Thanks chaps! Jason has hit the nail on the head, because the ball sits in a cradle in the arm drilling/pinning/Loctite is pretty much out.
Jason, they were from an ebay seller – Hardened stainless steel grade AISI 420, hardened to Rockwell HrC52-55. I'm thinking it will cost more to get the suitable "solder" than its worth so may well go for the brass balls.
Andrew, it had crossed my mind to remake the arms and incorporate the weights in them or just make a steel rod and solder that on maybe. No rush, I'll ponder on it while I make some of the other parts.