Transferring Large File (EBCDIC) from LAN to mainframe

We are experimenting with moving file archival from the mainframe to the LAN as a way to reduce operation costs.

I can transfer files from the mainframe to the LAN using FTP, which works if the file is tape or disk, or the Micro Focus Drag N Drop tool when the file is just disk. My problem arises when I'm trying to return a file or files back to the mainframe in instances where we need to perform a re-run, recoveries, etc.

When I try to FTP, the transfer fails with large files because I can't allocate enough space using command-line FTP. Does anyone know how to perform space allocation and a file transfer using the Windows FTP command line client?

Thanks!