Hard drive locking is a feature of the IDE/PATA spec but a rarely used one so not everything implemented it, especially not hard drive readers/adapters, hence the x-pec compatibility list (
https://xboxdrives.x-pec.com/?p=list ) and need for a computer with it on the motherboard to do anything with in all the guides.
The locking key in the case of the xbox is contained within the EEPROM files and can be read from a softmodded machine (not sure there is an option to grab it via some reader either). This is then considered unique per console.
Hardmods (chips and TSOP) jump in before the BIOS runs and thus can skip the locking stage (thus can use any drive they like).
Softmods (save exploits and drive swap) come in after the BIOS runs and thus have to be able to lock and unlock to get through that portion.
If it had come directly out of the former then you might well have been able to play with something from
https://xbox-hq.com/html/downloads-cat59.html or whatever FATX (the slightly tweaked version of FAT drive format that the xbox used and possibly further tweaked for the 360). If you had stuffed it into a softmodded machine it might well have locked it with its own key (possibly having seen the modded dash and deciding it was not a valid dash -- the softmods would install exploits and keep a minimal version of the original dash before jumping to a homebrew one, if you control the BIOS then who cares just go for the good stuff). If you have a motherboard with IDE in still available to you then by all means try some of those or whatever comes up from a search as it is not likely to be a long affair.
Most of the xbox drive format capable software should be smart enough to see if something is encrypted or not rather than just have it as a default assumption that you have to enter a dummy code for.
A mod chip in some xbox out there is unlikely to do anything for you if it is already locked with some unknown key.
To this end we are back to seeing if someone out there has a means of bypassing IDE drive locking. I fully expect there to be something (it is a seldom used security feature that not everything even bothered to implement and only considered a part of security rather than whole deal and made for hard drive format that was old at the time where hard drive processors probably have less power than many watches today... I would be truly stunned if there was not a exploit to bypass things), however I don't know of anything in particular having appeared in public xbox circles.
https://xboxdevwiki.net/Hard_Drive#Locking_Mechanism has a tiny bit more if you did want something. Assuming you can run it against a file rather than the drive that would be within reason for a brute force attack (possibly guided by needing to be combined with serial and model number). If you have to try it against the drive and wait for it to spin up and down then rather less so.