Most of the interpreters are provided as assembly source code (for the 6502, Z-80, and so on). Some have compiled binaries as well. As with the Infocom game source code, what's available is what's available.
This repo contains a small amount of internal documentation, mostly about how to create working floppy disks for each platform. It contains no personal or private communication, unless you count one footnote about a "straightforward" porting job.
Many directories include a large "assembled printout" file (usually .prn or .lst). This is a text file containing the assembler output for a complete program, both hex bytes and opcodes. ("prn" because it is notionally formatted for a line printer.)
The unix directory contains a C implementation of DIP, the virtual machine used to implement Fooblitzky. The atari and ibm directories contain assembly implementations of same. unix/foo.dat is the game file in question; unix/ediptst.sum would be a test suite game.
(Wikipedia refers to this as "GZIP - Graphical Zork Interpreter Program". I'm not sure what the origin of that name is. It doesn't appear in the Infocom source as far as I can tell. A couple of files refer to it as "GRIP" or the "G-machine". I'll stick with "DIP".)