Hi Pom Pax,
I'm not sure what floats were used by Francis Chichester but didn't he pick them up cheap from a dockside somewhere?
I recall that he tested them by filling them with water and nothing leaked so he set off on his crossing for Norfolk Island (or was it Lord Howe Island first?). Overnight the aircraft sank. Water was able to get into the floats but not the reverse. He had to rebuild the aircraft to continue the Tasman crossing..