I think you are missing the options for your keyboard and pointing device, among others.
I would just do a "grep Option /var/log/Xorg.0.log", change the options which imply udev's usage, and write all options in the config file. Else you can take xorg.conf-vesa as a basis.
In addition you will have to populate yourself the /dev directory and load all the kernel modules you need, but I assume that you are well aware of that.
There may be other caveat, like you won't be able to use an initrd to start Linux (it seems).
FWIW I quote below CHANGES_AND_HINTS.TXT from Slackware 13.37:
The Slackware installer uses udev to initialize your hardware, including the
network interface card(s). This has positive consequences for network
installations (using NFS, FTP, HTTP or SMB). You no longer have to run the
'pcmcia' and 'network' scripts prior to running 'setup' - the network
interface will be created and intialized by udev. If a DHCP server is
found on your local network, the setup program will let you choose between
automatic configuration of your network interface using DHCP or specifying
a static IP address. Using udev, the commandline for fully unattended
configuration and startup of the dropbear SSH server has changed slightly.
Suppose you want to boot the 'hugesmp' kernel, use DHCP for interface eth0,
and you have a us-english keyboard layout: the commandline to auto-start
the SSH daemon in the installer would become:
hugesmp.s kbd=us nic=auto:eth0:dhcp
Note: if you do not want to use udev, the "auto" keyword in that example
commandline must be replaced with the actual name of the network module for
your card. If you do not want to use udev, you must add the parameter
"noudev" to the command line that boots the Slackware installer, and the
original ("old") Slackware hardware configuration scripts will be used.
Also note that this is not supported...