If Disk Utility can mount the System 7 floppies, then it should be able to write those disk images to the floppy diskette. Assuming, of course, that your floppy drive is compatible with the OS. (Is this true with OS X?) At least with respect to DiskCopy 4.2 images, the software creates an image of the entire floppy. I'm fairly certain that later versions work in the same way. (Though later versions can handle compression of images, and non-floppy disk images.)
If worse comes to worse and those are Disk Copy 4.2 images, you can strip off the header and copy them to floppy using dd, as Paws suggested.
To my knowledge, there is no such thing as a boot block on a Macintosh floppy diskette. The Mac's firmware is aware of the HFS file system and looks for a special flag on that file system, which says the folder is "blessed" (i.e. it contains the system folder).