What does it mean to have "custom access"?
Generally, the "You have custom access" can indicate that the file has more complex permissions set than the Finder's Get Info window can display. From this Apple support article:

Custom: If the permissions for an item is set to Custom, the permissions have been configured in a way that is more complex than is provided in the basic user settings.


It's possible that the files on your SMB server have Access Control Lists setup. You may be able to get additional information about these (non-POSIX) permissions in OS X by using a command like ls -ale /Path/To/Folder.

It's probably also worth noting that the Finder may have problems setting permissions on your SMB share. I'd probably recommend configuring some sort of server-side permissions inheritance (i.e., using ACLs) to keep permissions in check on your share.