Yes, I've been installing Apple changes into GNU Objective-C for the
past month or so. Interestingly, most of the major differences are
already
in standard GCC 2.95.2, if you say -fnext-runtime; most of Apple's local
changes are connected to PDO and other NeXT activities that have been
abandoned, and those are not going into FSF GCC.
That said, the runtimes are spectacularly different and are going to
stay
different for some time I suspect, but in the case at hand, if you're
just going to translate message sends, that doesn't require a whole lot
of runtime knowledge.