M8350 is the interface from the Omnibus to the positive (TTL) I/O interface first used in the PDP8/I. It is used to interface to the rack of modules style interfaces. There is a related Data Break (ie. DMA) interface card M8360 As I suggested before, you want to watch for the 8/A RL interface card The RX8E floppy card intf part number is M8357 http://www.cs.uiowa.edu/~jones/pdp8/hard8e/modules.html for a list of modules. Again, watch for cables. Omnibus cables are useful, as are the over-the top board connector blocks. Omnibus cables LOOK like Unibus cables (but they aren't...) Easiest way to tell is Unibus cables have a section of the paddle edge connector fingers connected together with a big PCB trace