Right, but you are saying when I boot from the emergency disk and install the drive that way, the 120GB will show up?
The basic rule is you need support for larger harddrives being active in order to see the full capacity. The driver in Kickstart only supports 8 GB.
In order to change the partitionable area of a HDD you have to go to the "install drive" part of HDToolbox. Doing so will delete all existing partitions. If you want to keep the existing partitions and only add the additional space, you should use FixHDDSize.
And with 'if you install the HHD like this', you mean, without using the emergency disk?
I mean with the original Kickstart IDE driver scsi.device V40.
If you don't like the idea of an emergency disk you can also install OS 3.9, reboot and then install the HDD again. But that's much more work.
Or should I replace scsi.device? Its dated 12/21/1993, surely that is not the one IDEfix has installed for me?
I don't know the dates. Check the version number.
V40 -> unpatched Kickstart version
V43 -> version of OS 3.5 or 3.9
V116 or higher -> IDEfix
Realising that you got an IDEfix Express, I am not sure how much software support it needs. Whether the IDEfix software is needed or not. If it is needed make sure that scsi.device is version 116 or higher and not 43 or below.
Or should I enter my harddrive details manually?
You cannot force the HDD being big. If you enter values which are larger than what the driver can see, it will not work. You should first make sure that the updated driver is active. An indication that it is not active is that HDToolbox shows you exactly 16383 cylinders, 16 heads and 63 sectors. That's the maximum scsi.device V40 can see.
If HDToolbox shows bigger values but still not the entire 120 GB, you should consider to enter the values manually. Or use FixHDDSize, that's easier and safer. Nothing to do with lazyness, sorry for that.
Or should I install OS4 instead?
If OS 4 boots from floppy/CD, you can use MediaToolbox to install the HDD. But when booting OS 3.9 after that, you still have the problem that the driver to see the entire capacity needs to be made active.
BTW, does it work with WB 3.1 + IDEfix ? But the same applies here: you first have to install / run IDEfix, then you can install the HDD with its full capacity.