cannot find libnautilus-extension in the repo just libnautilus and dbg which I take as for debugging. and I am not knowing what I'll be lacking with Dropbox if I figure out how to modify that PKG_CONFIG_PATH and CFLAGS and get it to install as I'd like to have the complete package installed

checking for NAUTILUS... configure: error: Package requirements (libnautilus-extension >= 2.16.0) were not met:

No package 'libnautilus-extension' found

Consider adjusting the PKG_CONFIG_PATH environment variable if you
installed software in a non-standard prefix.

Alternatively, you may set the environment variables NAUTILUS_CFLAGS
and NAUTILUS_LIBS to avoid the need to call pkg-config.
See the pkg-config man page for more details.