This is a wonderful find, is it possible for you to read the other tapes also?
I would be particularly interested in the early 8080 compiler, I am actively working on something like that at the moment. I have quite extensively reverse engineered the famous Ritchie PDP-11 C compiler to figure out how it works, it is actually pretty straightforward and I may write a document about it someday (the code is a bit horrible due to the many exceptional cases added to improve the output in particular situations, all this has to be ignored in order to get at the underlying algorithm which is elegant).
Steven Schultz or someone else also seems to have begun a PDP-11-targeted port of the of 4.3BSD VAX-targeted PCC backend, I can't see myself completing this but I was considering trying to adapt the Ritchie pass2 to understand PCC intermediate code instead of Ritchie pass1 intermediate code and using it more-or-less as-is as a PCC backend. There is no requirement that a PCC backend use the PCC instruction table or macro format and in this case it would probably be simpler if it did not. But one or other of these backends has to be ported to Z180 (~= Z80 ~= 8080) and I'd be thrilled to have a starting point.
I will also eventually pick up the 68K compiler too although I believe some pretty good PCC based 68K C compilers will be extant due to late versions of BSDs having been developed on 68K (I could be wrong about the BSDs and 68K but I am sure many unices ran on 68010+ and even a few on 68000 using the famous second CPU chip to handle faults).
cheers, Nick