I have received qualified permission to publish the MUSS source code that was recently recovered, as free and open source software. It is available here.
I have also made a bit of progress on the MUSS restoration. My implementation of FLIP is improved but still not quite there yet. I also have a parser for MUSL, which parses the output of my FLIP implementation for one of the FLIP source modules, with a little hand modification before parsing it.
I have created a page on MUSS where I will report more about MUSS and its restoration.