For my PC01 the rails can be seen here (third from top). Sounds like the PC04 rails are similar. They have an added plate to make the rack attachment stronger since they don't bolt at the back. http://www.pdp8.net/shows/vcfe08/pics/booth3.shtml http://www.pdp8.net/shows/vcfe08/pics/showing.shtml Normal rails work fine, my PC04 didn't have any so I used normal ones that attach both front and back. You can see that in the next picture. For the TU56 I cheated. I mounted angle iron below it which I can slide it in on and then bolt at my leisure. The drive has a lip which makes things a little strange but works pretty well. I used aluminum but that is messed up by sliding the drive. http://www.pdp8.net/shows/tcf05/pics/big_stuff.shtml?small The maintenance manual says how it is supposed to be installed. It has a a support bracket between the rails the drive rests on. (pg 2-3) http://www.pdp8online.com/pdp8cgi/query_docs/view.pl?id=27