What you need, a vanilla copy of the original disk?
That will be easy if you have the disk.
Yes, but I don't have any original discs...
But: I am an idiot. After having disassembled a part of the 8088 based FDC controller ROM with the formatting routine, I found the cause why it was refusing to accept the FlashFloppy Gotek emulation as a real disc. And of course everything has already been presented to me, I just didn't catch it:
Cylinder 78 head 1 is formatted using a track id of 150 in the sector headers, not the usual 78. Of course this information was already hidden in the Teledisk image. And I read through the dump but didn't find it as the track header inside the dump was using the correct cylinder numbers, but the sector headers did not (In fact there is no such thing as a track header with track ids on the disc, the track preamble consists of 80 bytes 0x4E, 12 bytes 0x00, 3 bytes 0xC2 with missing clock transistion between bits 3 and 4, 1 byte 0xFC index mark, 50 bytes 0x4E). All other used tracks have the correct track id in the sector headers, even the cylinder 79 using different sector ids. And the raw images cannot handle such track ids, as the sector headers are generated on the fly by FlashFloppy, using the cylinder that is stepped to.
After some discussion with Keir Fraser he suggested to use HFE format instead. And that works like a charm. I created an empty image and formatted it in the 4952A. And then converting the Teledisk format to HFE (with patching the data rate as it was taken with a PC drive) immediately worked too.
BTW: The HP firmware programmer must have smoked something silly. They coded a simple negation for the head select as follows (CL contains 0x00 or 0x01):
f000:9279 f6 c1 ff TEST CL,0xff
f000:927c 74 02 JZ HEAD0
f000:927e b1 ff MOV CL,0xff
HEAD0 XREF[1]: f000:927c(j)
f000:9280 fe c1 INC CL