Note that although both AMOS and A-Shell store the user database in the file OPR:USER.SYS, the file layouts are not compatible. Thus you'll have to manually enter all the users when porting from AMOS. Also, several of the AMOS-centric fields in the USER.SYS are ignored.
Also note that when you use LOGON to log on as a user defined in the USER.SYS database, A-Shell will replace the native operating system logon name with the name specified in LOGON.LIT. This name will apply within A-Shell, but will not affect the real identity of the user from the host operating system perspective.