My SFI in the AudioTechnica RE70 (trying to fake a ATH-2) definitely don't have much treble to it. Which is weird compared to how the SFI's react in those AKG shells.
I might have a clue on what's causing it but as far as I can tell, I can't increase the treble even by plastering the back with reflectors.
My guess is the ~1mm closed space between the drivers and the baffle. And perhaps the holes on the baffle which do not necessarily align.
Pretty sure they won't. YH-1 drivers are just that big.
And as you may have noticed from the thread, you're not going to get the same sound just by dropping the drivers in a different enclosure; you'll have to make considerable modifications to get them sounding right. Where, there's always lucky cases of something that makes it sound perfect, but don't count on that being the case. Be prepared to have to damp it somewhat.
From the looks of it you're looking for open-back headphones to place them in?
How about using the same headphone as BMF?
If he was able to fit TDS-15 drivers inside, the YH-1 will fit. Although you can see he made new baffles and did a lot of cutting.
Or if you don't mind the looks, see if you can find one of the headphones in this thread:
The ones mentioned all OEMs of each other, but I know at least that the YH-1 drivers could fit in my Dero-D560 (one of the OEM headphone)