Why not put a single linux machine (i.e. plug computer, or other embedded device) to take the telnet/ssh session, and a bunch of cheap I/O control devices (possibly arduinos) to it to control the machines? For example, you can get a teensy (http://www.pjrc.com/teensy/
) which has USB slave support. You can connect 128 of those to a single USB port on your linux box, so you could theoretically control 128 machines with 128 teensies. If you want to control 50 machines, You'll spend 1000 bucks just on buying a bunch of teensies though, and obviously cabling would become a problem as you'd have to run a bunch of USB wires through your basement and set up hubs everywhere
Also, if you use a USB protocol to communicate with the I/O device, you have an added bonus of separating the UART stream to/from the vax from other I/O such as reset, power on/off, etc. You could also solder input pins to the leds so you can even monitor led status upstairs.