Guys... this is an issue with the protection that also happens on some original Amigas with different drive models. The protection uses a trick to create "no flux" areas. The bad thing is that this has to do with the analogue preamp being fooled with. As I said in other threads it's extremely dangerous to do so because results can vary.
This protection is used in an earlier Copylock by Rob Northen and I guess we now know the reason it was discontinued and replaced by the "popular" density based protection.
Just avoid drives that don't work.
The mod is just the standard mod applied to PC drives; like line swapping (mainly for READY and some other stuff). You can basically test if a drive has been modded successfuly, if e.g. the Giana Sisters loader (talking of the crack here) works or not. It relies on the ready signal.