RH will allow this - simply make the install disks, boot and load the network card and do an nfs install from RHat. Its still slow but <3 days on ISDN unless you install everything.
We have a number of servers in the US and now moving to the UK, builds have always been an issue as we have totally customized Slackware installs.
The method now is an install using 2 disks a custom boot disk and a custom root disk.
Once the root disk has loaded, we use sfdisk to partition the drive, the install script then converts the partitions to use "reiserfs".
It then mounts the hard disk, connects using ftp (nsfptget) pulls down a text file listing the packages to install, it then loops through downloading the Slackware packages. Installs them one by one.
It then pulls down some custom tar.gz files of the main directories (home,etc,usr/local,sbin,bin etc..) and extracts them onto the HD
It then runs Lilo unmounts the HD and asks for a reboot.
One reboot later and its up and running. Each server is identicle and a build takes less then 10 mins. Its easy to edit a system and recreate the FTP files etc..
We also run a program that mirrors the slackware distro so we always have the latest slack packages.
Simple but effective
Regards Darren