First, there's no need to post this twice. If you must ask the devs directly, use the oss-devel
Second, I can't speak for the devs, but I suspect they'll have no objections in principle. I did a diff on the port, and noticed a few marginal issues:
A) The build system can be modified in a less intrusive manner (e.g. use OSflags in srcconf.c to set -DOSS_NO_LONG_LONG instead of editing the .config files).
B) speaking of long long, a typedef may be preferable to lots of #ifdefs (But perhaps better to ask the devs about this first).
[Edit: I'll leave reviewing the grc3 changes to someone more informed]
C) Why was ossdevlinks modified to call system("rm..") instead of unlink() calls?
[Edit: I also suggest breaking up any commit to discrete changes. e.g. C++->C comment changes, OSS_NO_LONG_LONG changes, minix-wrapper, etc.]