That mention of A=435 pitch was very useful.

I have a pair of recorders in D (tenor, voice-flute) and A ("sopralto") made for Peter Harlan in Germany about 100 years ago. That was the kind of recorder Paul Hindemith wrote his "Ploener Musiktag" trio for - it's one of the classics of 20th century recorder repertoire, but is never played now on the original instruments and as far as I know, no recording at that pitch exists.

I haven't had much luck playing the D one in tune. The A one does work, pretty loud. But when I try A=435, they work just fine, and I'm playing the A one at a more reasonable volume to balance the D. So, thanks for the hint!

Incidentally the pitch of that "scientific" fork is a just intonation A above the 256Hz C, not an equally tempered one. Probably once part of a set intended for experimenting with JI.