I assume that it is a Macintosh SE FDHD.
In order to ensure that a floppy becomes bootable, it is always best to create it directly from the downloaded disk image using Disk Copy. In Disk Copy 4.2 this means via the Make A Copy button (in 6.3.3 the Make a Floppy command in the Utilities menu).
It is wise to avoid too many steps, especially with modern/other operating systems involved. Do you have access to another older working Mac with a built-in floppy drive? If so, you should be able to download files through your PC, and transfer them as they are to that Mac (you may need a PC utility for the handling of Mac disks, if the receiving Mac does not have PC Exchange or Apple File Exchange installed). Then use the Mac to produce a bootable floppy. Certain PC utilities for Mac disks may have the option to decode MacBinary at the same time as the transfer is carried out. Otherwise, StuffIt Expander will be needed on the Mac.
It may be easier if you choose one of the British English 7 or 7.0.1 systems, since these have been made available for download as individual floppy-sized files (no need to open/mount an smi first).
If the SE FDHD is working OK under System 6, it may even be possible to use Disk Copy 4.2 for the creation of a bootable floppy there.
Also, a way of making a disk containing a StuffIt Expander installer for Mac on a Windows PC could perhaps be of some interest: