If your FastFileSystem file is much larger than 20 KBytes, or the version number shown is in the range 37-40 (or higher) then it cannot be used under Kickstart 1.3.
I am aware that you should know best because you have the possibility to look at the source code, but nevertheless I have to disagree here. FFS V40.1 works well on Kick 1.3 in INTL mode, at least for reading. The only disadvantage is that each partition gets a second icon labelled DH0: DOS[].
From personal experience, you might want to use HDInstTools (check AmiNet, v6.9 should be the last stable one) to recognize disk geometry, edit partition(s) and load proper filesystem into RDB. It has more control over configuration process that might be more valued later, if some problem arises.
HDInstTool is the only partioning tool for the Amiga which does *not* work correctly. It works as long as you accept the geometry it calculates but as soon as you try to use a different geometry or even worse if you try to edit a partition table created by another tool, it fails miserably, usually deleting all partitions.
Regarding control, HDToolbox is the tool which gives control about everything in the partition table. HDInstTool does not give as much control. And if a problem arises, HDInstTool is the last tool to use because of the reason mentioned above.
HDInstTool is only good if you are absolutely sure that you never used a different program to edit the partition table you want to edit now.
