I know you have probably solved this by now. However if I were going to be doing something like this, and I have, I would not download the data in EBCDIC. I would create a custom translate table on the z/OS side and then use FTP, with SSL enabled of course, in TEXT mode and let z/OS translate the data from EBCDIC to ASCII.

Or if you have one of PKWare's or Data21's "ZIP" programs, create a custom translate table for it and compress the data as text and let them convert from EBCDIC to ASCII. Then download the compressed file in binary mode.