On z/OS, the FTP SITE and LOCSITE commands have a few extra options for ‘traditional’ z/OS files (as apart from z/OS UNIX files). They’re documented in the z/OS Communications Server IP User’s guide.
So from your remote UNIX machine, you could use the FTP command
SITE RECFM=FB LRECL=180.
If this doesn’t suit, another option is to pre-allocate the dataset on z/OS.
Hope this helps.