I don't know how the later versions of the USB adapter differ from the first, but ISTM that the earlier version could be upgraded by replacing the SN74AHC1G14 IC nearest to the HDD header with an MC74VHC1GT04 or SN74LV1T04.

MC74VHC1GT04, ON Semiconductor, Inverting Buffer / CMOS Logic Level Shifter, 1.8V to 3V logic, TSOP-5, Vih = 1.4V, Vil = 0.53V @ 3.3V:
https://www.onsemi.com/pub/Collateral/M ... GT04-D.PDF

SN74LV1T04, Texas Instruments, Single Power Supply Inverter Gate CMOS Logic Level Shifter, 1.8V - 5.5V, SOT-23(5), Vih = 1.35V, Vil = 0.8V @ 3.3V:
http://www.ti.com/lit/ds/symlink/sn74lv1t04.pdf

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A backup a day keeps DR away.

Out of curiosity : would an adapter modified in this way still work with older drives that use 2.5/3.3V ?

Yes. The point is that any input greater than Vih will register as a logic HI, and any input less than Vil will be seen as a logic LO.

_________________
A backup a day keeps DR away.