These are all the associated files I have found for my Compaq 386S.

I have included a disk label reproduction for the DIAGNOSTICS diskette that I made based on the design of a similar diskette I found. 
If anyone has the original disk, please send me a scan so I can reproduce the original disk exactly!

SP308.EXE contains the program to generate the 720K diskette. It doesn't have to be a 720K diskette, but can be a 1.44MB disk 
that's been formatted in a retro computer to 720K... later windows don't seem to be able to do this!

Included also is an image of a 1.44MB disk made to these specifications if you can't run the EXEs.

I have also found out that if you need to replace the IDE cable, it has to be a 40 wire straight through cable (as in, not one of the more modern/faster 80 wire.

They are quite difficult to find, however I have found you can buy the appropriate IDC connectors and a 40 wire ribbon cable and easily make a cable yourself (to size) 
Doing that that will support both Primary and Slave drives.

If you want to use a custom HDD type, download ONTRACK Disk Manager 9.57 - either copy the disk image to a floppy with WinImage 
or use a Windows XP machine to create the floppy with the exe

Thanks to Phil's Computer Lab for the downloads of the version of ONTRACK that I've successfully used on my 386S (with both a 1GB compact flash card and a 40GB IDE hard drive, 
but remember in MS-DOS 6.22/ FAT-16 drives only 8GB is usable at most, and you have to make 4 partitions of 2GB to get this working)

I'll be making a blog post on my website in the future about all the things I have found with my Compaq 386S, but these are the important ones to get started.