This is probably a bit late now, but have a look through {link} and it may answer your question. While the second answer relates to 58mm baskets, in my experience variations of one degree or another exist at all sizes. I can't speak for other manufacturers, but the first link outlines the method I u...

Just a point of clarification; Pullman tampers are supplied to whatever size is best for the customer's baskets. 58.3mm is just the size provided for the Roadshow