Firstly, the current gr-op25 recipe in pybombs will build a version of
OP25 that’s compatible only with GNU Radio version 3.7. (If one really
wanted to build OP25 for GR3.6 he could pull the old SVN repo which is
still online, but that version is no longer maintained). However (last
I knew) no one has gotten gr-baz working with the newer versions of
OP25…
Second, the fsk4 module is accessible in gr-op25 - assuming gr-op25 is
correctly installed you should be able successfully to do this in
python, as a test- from op25 import fsk4_demod_ff
Third, the process of getting these things more integrated generally,
and ultimately into GRC, continues. There’s more work to do on this,
but if you want to see a complete example py hier block that
encapsulates the FSK4 demodulator, see this link:
http://op25.osmocom.org/trac/wiki.png/browser/op25/gr-op25_repeater/apps/p25_demodulator.py#L71
[Note that if you pull the git repo you should checkout the ‘max’
branch]
Finally, last but not least, Marcus M., it was great to meet you in
person at the most recent GNU Radio conference in Wash. D.C. You
probably don’t remember me, I was one of the few geeky looking guys
there. And thanks for pointing out, we do need to update the to do list
in the wiki - the documentation always seems to lag behind 
73
Max Parke