I recall my original kit from 40 years ago was Wills, it had a Belpaire boiler and I paid someone at the time to retro-adjust to the original round top, including sourcing the safety valve.
@PenrithBeacon, found it thanks, and will order.
@Compound2632, all I wanted was the part name and source and I end up with a whole lot of extra knowledge as I often do from your posts, fascinating.
Cheers all.